-NRLF 


B   M   ESE 


GIFT   OF 

Kancroft 
LIBRARY 


SCIENCE  FOR  THE  PEOPLE. 


No.   I. 

THE   UNITY  OF  NATURAL   PHENOMENA. 

BY  EMILE  SAIGEY. 


cc'e  '  c  ^    '  c  c    c  c  e  o  ^  Cc  <  c  *'  *  N     P  R  E  S  S  : 

THE  SCIENCE  AND  PHENOMENA   OF  HE  A  T. 

From  the  French  of  AMEDEE  GUILLEMIN. 


THE   PHENOMENA     OF    PLANT  LIFE  AND   SEX- 
UALITY OF  NATURE. 

BY  L.   HARTLEY  GRINDON. 


THE  PHENOMENA    OF  SOUND. 


THE   UNITY 


OF 


NATURAL  PHENOMENA. 

A  POPULAR  INTRODUCTION  TO  THE 
STUDY  OF 

THE  FORCES  OF  NATURE. 

FROM   THE   FRENCH   OF 

M.  EMILE   SAIGEY. 
// 

WITH 

AN    INTRODUCTION    AND    NOTES 

BY 
THOMAS  FREEMAN  MOSES,  A.  M.,  M.  D., 

PROFESSOR    OF    NATURAL    SCIENCE    IN 
URBANA    UNIVERSITY. 


BOSTON : 

ESTES    AND     LAURIAT. 
-'S73- 


•  Entered,  according  to  Act  of  Congress,  in  the  year  1873, 

BY  ESTES  AND   LAURIAT, 
In  the  Office  of  the  Librarian  of  Congress,  at  Washington. 


GIFT  OF 

flam:  roil 
LIBRARY 


Stereotyped  at  the  Boston  Stereotype  Foundry, 
19  Spring  Lane. 


CONTENTS. 


PAGE 

TRANSLATOR'S  INTRODUCTION 9 

AUTHOR'S   INTRODUCTION -23 

CHAPTER  I. 
THE  GENERAL  HYPOTHESIS.  .         .        .         .        %  31 

I.     Atoms  and    Motion.  —  Physical  Phenomena  may  be  reduced  to  a 

single  Principle,  and  considered  as  the  Effects  of  Motion. 
II.     The  Hypothesis  of  the  Unity  of  Natural  Phenomena  in  its  Relation 

to  Science. 

III.     The  Difficulty  encountered  by  endeavoring  to  express  New  Ideas  by 
Means  of  Old  Terms. 

CHAPTER  II. 
SOUND  AND  LIGHT.        .        .        .        .        .        .        .        -55 

I.     Nature  and  Mechanical  Equivalent  of  Sound. 

II.     The  Nature  of  Light  and  of  Interference.  —  Universality  of  this  last 
Phenomenon. 

III.  Conclusions  as  to  the  Ether  drawn  from  Luminous  Phenomena. 

IV.  What  does  the  study  of  Light  teach  us  concerning  the  Molecular  Con- 

stitution of  Bodies  ? 

CHAPTER  III. 
HEAT. 98 

I.     The  Dynamic  Theory  and  Mechanical  Equivalent  of  Heat. 
II.     Changes  of  State  produced  by  Heat  furnish  Information  as  to  the 

Constitution  of  Bodies. 
III.    Theory  of  Gases. 


861372 


8  CONTENTS. 

CHAPTER  IV. 
ELECTRICITY.  ..........     126 

I.     It  is  necessary  to  determine  the  Electric  Unit,  a;id  to  find  its  Me- 
chanical Equivalent. 

II.     The  Electric  Current  apparently  a  Transport  of  Ethereal  Matter. 
III.     Electricity  and  Light :  their  Mutual  Relation. 

CHAPTER  V. 
THE  ATTRACTIVE  FORCES.      .......     154 

I.     Points  of  Resemblance  and  of  Dissimilarity  presented  by  Gravity, 

Cohesion,  and  Chemical  Affinity. 

II.     Gravity  may  be  considered  as  an  Effect  of  the  Motions  of  Ether  and 
of  Ponderable  Matter.          • 

III.  Historical  Notions  regarding  the  Idea  of  Universal  Attraction. 

IV.  Hypotheses  in  regard  to  the  Formation  of  Worlds  and  the  Origin  of 

Gravity. 
V.     The  Molecular  Agencies,  Cohesion,  and  Chemical  Affinity. 

CHAPTER  VI. 
LIVING  BEINGS 205 

I.     Vital  Activity  consists  in  the  Transformation,  not  in  the  Creation,  of 

Motions. 
II.     The  Manner  in  which  the  Laws  of  Thermo-dynamics  are  Verified  in 

the  Case  of  Animated  Beings. 
III.     Muscular  Contraction  and  Innervation. 

CHAPTER  VII. 
CONCLUSION.    . 232 


TRANSLATOR'S  INTRODUCTION. 


SINCE  the  discovery  of  the  laws  of  gravity,  more 
than  two  hundred  years  ago,  no  scientific  achievement 
has  been  so  fruitful  in  results  as  the  determination  of 
the  mechanical  equivalent  of  heat.  In  1842  Dr.  May- 
er, of  Heilbronn,  in  Swabia,  demonstrated  that  the 
blow  of  a  hammer  weighing  four  hundred  and  twenty- 
four  kilograms  upon  an  anvil,  with  the  velocity  it  has 
acquired  by  falling  through  a  distance  of  one  metre, 
produces  an  elevation  of  temperature  equal  to  one 
degree  centigrade.  This  experiment  has  wrought  a 
marvellous  change  in  all  our  conceptions  of  Matter 
and  Force,  and  still  gives  promise  of  results  which 
the  imagination  fails  to  grasp.  It  is  now  considered 
as  demonstrated  that  heat,  electricity,  light,  magnet- 
ism, chemical  attraction,  muscular  energy,  and  me- 
chanical work,  all  are  but  exhibitions  of  one  and  the 
same  power  acting  through  matter.  The  molecules 
of  matter,  variously  stirred  by  this  all-pervading  force, 

9 


IO         UNITY  OF  NATURAL  PHENOMENA. 

:  ar^  throwm  fejto^ weaves,  which  strike  against  our  senses, 
the  motion  £hus°<  communicated  to  our  nerves  im- 
s  cavs  "heat,  sound,  or  light,  according  to  the 
rapidity  and  breadth  of  the  undulations.  If  an  undu- 
lation of  one  sort  is  interfered  with,  another  immedi- 
ately succeeds  of  exactly  the  same  strength.  Light 
ransforms  itself  into  chemical  action,  this  into  heat, 
md  heat  into  motion.  Finally,  all  these  modes  of 
motion  are  not  only  mutually  convertible,  but  they 
may  also  be  turned  into  mechanical  work.  The 
amount  of  work  which  a  fixed  quantity  of  each  can 
do  is  termed  its  "mechanical  equivalent."  In  other 
words,  force  is  a  constant  energy,  never  increasing  or 
diminishing  in  absolute  value.  It  is  like  a  stream, 
now  flowing  through  uninterrupted  channels,  silently 
and  imperceptibly,  now  thrown  into  gentle  undulations 
as  it  comes  into  contact  with  the  subtle  forms  of  mat- 
ter, and  now  giving  striking  displays  of  its  power  as  it 
meets  with  greater  resistance.  Light,  sound,  heat,  the 
invisible  flow  of  the  terrestrial  magnetic  currents,  as 
well  as  the  aurora  and  zodiacal  light,  the  flow  of  the 
sap  in  plants,  and  the  circulation  of  the  blood  in  ani- 
mals, are  all  exhibitions  of  this  single  Force. 

From  the  unity  of  Force  the  induction  was  easy 
and  natural  to  the  unity  of  Matter.  The  whole  ten- 
dency of  modern  physical  science  is  to  do  away  with 


TRANSLATOR'S  INTRODUCTION.       u 

the  notion  of  an  indefinite  number  of  primary  ele- 
ments, and  to  substitute  instead  a  smaller  and  smaller 
number  of  primitive  forms  of  matter.  We  must  ad- 
mit, however,  that  this  notion  is  not  strictly  a  modern 
one,  for  the  idea  that  matter  is  identical,  and  only  its 
forms  various,  is  as  old  as  Aristotle.  The  results  of 
experimental  investigation  at  first,  and  for  a  long  time, 
cast  discredit  upon  this  ancient  doctrine,  but  modern 
chemical  and  physical  research  serve  only  to  confirm 
it.  Thus  a  great  cycle  of  human  thought  is .  com- 
pleted. 

What,  in  brief,  is  the  theory  of  modern  science  in 
regard  to  matter? 

By  changes  in  the  mode  of  aggregation  of  the 
atoms,  which  changes  depend  chiefly  upon  the  degree 
and  kind  of  motion  with  which  they  are  endowed, 
matter  appears  to  us  under  certain  definite  forms-,  as 
water,  air,  iron,  etc.  The  analysis  of  many  sub- 
stances, once  supposed  to  be  compound,  into  simple 
ones,  leads  naturally  to  the  conclusion  that  such  an 
analysis  is  possible  in  the  case  of  many  substances 
now  placed  in  the  category  of  elements.  That  won- 
derful class  of  elements,  the  metals,  would  appear  to 
be  the  most  stable  of  all ;  but  who  can  foresee  the 
result  of  spectroscopic  investigation  upon  these,  even  ? 
That  there  exists  among  them  some  common  elemen- 


12        UNITY  OF  NATURAL  PHENOMENA. 

tal  principle,  of  which  each  metal  is  a  variety,  is  an 
idea  already  broached.  A  comparison  of  their  char- 
acteristic spectrum  lines  may  afford  startling  results, 
surpassing  the  dream  of  the  alchemists.  Recent  ap- 
plication's of  spectrum  analysis  to  the  nebulae  and  fixed 
stars,  in  connection  with  the  theory  of  the  evolution 
of  suns  and  planets,  in  accordance  with  the  nebular 
hypothesis,  are  strikingly  suggestive.  The  spectra  of 
some  nebulae  give  evidence  of  but  two  elements,  nitro- 
gen and  hydrogen,  and  a  classification  of  the  fixed 
stars  and  nebulae  may  be  so  arranged  as  to  exhibit  a 
gradual  increase  in  complexity  of  structure.*  In  a 
word,  variety  of  form  and  unity  of  substance,  the  evo- 
lution of  the  complex  from  the  simple,  of  the  hetero- 
geneous from  the  homogeneous,  are  the  fundamental 
principles  of  modern  philosophy. 

The  author  of  the  following  Essay  assumes  that 
there  is  but  one  material  substance,  and  that  this  sub- 
stance is  the  Ether.  This  ether  is  the  primitive  and 
most  subtle  element ;  it  is  the  tissue  out  of  which  the 
entire  universe  is  wrought  —  a  kind  of  mineral  proto- 
plasm, in  fact.  This  theory  is  clearly  and  compactly 
stated  in  the  Author's  General  Hypothesis.  The  sub- 
ject of  the  ether  is  engrossing  so  much  attention  at 

*  See  an  interesting  article  in  Popular  Science  Monthly,  Janu- 
ary, 1873,  entitled  Evolution  and  the  Spectroscope.. 


TRANSLATOR'S  INTRODUCTION.  13 

the  present  time,  it  may  not  be  out  of  place  here  to 
mention  some  of  the  views  entertained  in  regard  to  it 
by  former  and  contemporary  writers. 

The  revival  of  the  doctrine  of  the  ether,  and  its 
support  by  many  of  the  most  eminent  physicists  of 
the  present  day,  is  a  remarkable  event  in  the  history 
of  science.  There  is  indeed  nothing  new  under  the 
sun.  The  ether  dates  back  to  the  early  days  of  scien- 
tific research,  and  first  occurs  as  a  subdivision  of  the 
air,  one  of  the  four  elements  of  Empedocles-.  It  is 
described  as  filling  all  the  interplanetary  spaces,  and 
also  as  penetrating  and  enveloping  the  particles  com- 
posing the  heavenly  bodies,  impregnating  them  with 
certain  effluvia  and  influences.  The  Greek -poet  Or- 
pheus hails  it  as  "the  bright,  life-giving  element" 
flowing  around  the  sun,  moon,  and  stars,  and  calls  it 
the  blastema,  or  universal  germ  of  things.  In  1664 
the  undulatory  theory  of  light  demanded  the  hypothe- 
sis of  a  homogeneous  medium  for  the  propagation  of 
the  light  waves.  This  theory  received  its  first  defi- 
nite statement  from  Huyghens,  in  1690.  Light  was 
judged  to  be  the  vibration  of  an  ether.  Even  New- 
ton, while  holding  to  his  emission  theory  of  light, 
acknowledged  the  probability  of  the  existence  of  such 
a  medium,*  and  speaks  of  the  universal  ether  as  the 

*' Whewell,  History  Inductive  Sciences,  vol.  ii.  p.  89.       4 


14        UNITY  OF  NATURAL  PHENOMENA. 

"sensorium  of  God."  Newton's  authority  in 'science 
served  to  hold  the  new  doctrine  of  light  in  abeyance 
for  more  than  a  hundred  years  ;  it  was  not  until  the 
beginning  of  the  nineteenth  century  that  it  was  placed 
beyond  a  doubt  by  the  labors  of  Dr.  Thomas  Young. 
Near  the  middle  of  the  eighteenth .  century,  while  the 
Newtonian  theory  was  yet  in  the  ascendency,  Sweden- 
borg  published  his  Principia,  in  which  he  maintains 
the  existence  of  an  ether  as  one  of  five  elementary 
forms  of  matter.  These  are  the  solar  vortex,  which  is 
the  cause  of  gravity  ;  second,  the  magnetic  element  ; 
third,  the  ether  ;  fourth,  the  atmosphere  ;  and  lastly, 
the  aqueous  vapor.  The  ether  is  the  third  of  these 
elements  in  the  order  of  succession,  proceeding  from 
the  sun  to  the  planets.  Its  vibrations  and  undulations 
are  the  cause  of  light  and  heat.  Motion,  diffused  from 
a  centre  through  a  contiguous  meaium  of  ether  parti- 
cles, produced  light  and  also  heat.  Our  earth  is  sur- 
rounded with  an  ethereal  aura,  the  position  of  which  is 
intermediate  between  the  solar  vortex  and  our  own 
atmosphere,  thus  serving  to  keep  up  the  contiguity  of 
expanse  between  the  sun  and  our  earth.  It  is  in  the 
state  of  ether  that  matter  has  become  "  sufficiently 
gross  to  be  perceptible  to  our  senses  by  its  effects." 
Swedenborg,  in  the  calm  and  philosophic  spirit  char- 
acteristic of  him,  took  no  pains  to  enforce  these  doc- 


TRANSLATOR'S  INTRODUCTION.  15 

trines  upon  the  attention  of  his  own  age.  This  indif- 
ference was  shared  by  his  contemporaries  at  a  time 
when  the  scientific  world  was  distracted  by  the  con- 
flicting theories  of  light.  In  1671  Leibnitz  published 
a  new  physical  hypothesis,  in  which  he  deduced  the 
causes  of  most  physical  phenomena  from  a  single  uni- 
versal motion.  The  particles  of  the  earth  are  endowed 
with  separate  motions,  which  give  rise  to  shocks,  from 
which  results  an  agitation  of  the  ether  radiating  in  all 
directions. 

Passing  down  to  our  own  times,  we  find  various  the- 
ories in  regard  to  the  ether.  That  of  Hartman  is  in 
substance  as  follows  :  There  are  two  kinds  of  atoms, 
ethereal  and  corporeal ;  bodies  are  made  of  spherically- 
shaped  atoms,  which  act  equally  in  all  directions,  the 
activity  proceeding  from  the  centre.  Between  the 
molecules  of  these  bodies  are  scattered  the  atoms  of 
the*  ether,  and  they  also  fill  interstellar  space.  The 
corporeal  atoms  have  a  tendency  to  converge  towards 
a  single  point,  but  are  kept  apart  by  the  ether  atoms. 
Between  the  corporeal  and  the  ethereal  atoms  a  mutu- 
al repulsion  exists.  Another  writer,  Spiller,*  calls  the 
"  world-ether  the  soul  of  the  universe."  By  such  an 
eminent  authority  as  Tyndall,  the  ether  is  recognized 

*  See  Article  on  Philip  Spiller's  Aetherism,  in  the  New  York 
Evening  Post,  January  24,  1873. 


1 6        UNITY  OF  NATURAL  PHENOMENA. 

as  the  interstellar  medium  filling  all  space.  "The 
luminiferous  ether  fills  stellar  space,  makes  the  uni- 
verse a  whole,  and  renders  the  intercommunication  of 
light  and  energy  between  star  and  star  possible.  But 
the  subtle  substance  penetrates  farther  ;  it  surrounds 
the  very  atoms  of  solar  and  liquid  substances."  And 
again,  "  The  intellect  knows  no  difference  between 
great  and  small ;  it  is  just  as  easy  to  conceive  of  a 
vibrating  atom  as  of  a  vibrating  cannon-ball ;  and  there 
is  no  more  difficulty  in  conceiving  of  this  Ether,  as  it 
is  called,  which  fills  space,  than  in  imagining  all  space 
to  be  filled  with  jelly.  You  must  imagine  the  atoms 
vibrating,  and  their  vibrations  you  must  figure  as  com- 
municated to  the  ether  in  which  they  swing,  being 
propagated  through  it  in  waves  ;  these  waves  enter 
the  pupil,  cross  the  ball  of  the  eye,  and  break  upon 
the  retina  at  the  back  part,  of  the  eye.  The  act,  re- 
member, is  as  real  and  as  truly  mechanical  as -the 
breaking  of  the  sea-waves  upon  the  shore.  Their 
motions  are  communicated  to  the  retina,  transmitted 
thence  along  the  optic  nerve  to  the  brain,  and  there 
announce  themselves  to  consciousness  as  light." 

The  essential  difference  between  the  foregoing  theo- 
ries and  that  of  M.  Saigey  may  be  stated  thus  :  In 
the  former  the  ether  is  regarded  as  filling  all  the  spaces 
between  the  stars  and  planets  and  the  atoms  of  bodies. 


TRANSLATOR'S  INTRODUCTION.       17 

M.  Saigey  believes  it  to  be  all  this  and  more.     He 

makes  it  also  the  constitutive  element  of  the  atoms 

• 

themselves.  "  The  atom  and  motion,  behold  the  uni- 
verse !  "  Such  is  his  enthusiastic  language.  Ether  in 
a  state  of  motion  fills  all  space.  The  ethereal  atoms 
form  societies,  which  are  the  molecules  of  bodies.  A 
body  is  a  collection  of  these  societies  of  molecules. 
Between  these  atoms,  molecules,  and  bodies,  exchanges 
of  motion  take  place,  which  constitute  heat,  light, 
chemical  affinity,  and  gravity.  These  exchanges  de- 
pend upon  the  relations  of  mass  and  velocity. 

Granting  these  premises,  the  remaining  point  in  M. 
Saigey's  hypothesis  —  that  the  laws  which  govern  the 
interaction  of  this  primitive  force  and  matter  are  none 
other  than  the  laws  of  mechanics  —  is  but  a  logical 
deduction.  These  laws  depend  upon  geometrical  rela- 
tions, and  may  be  mathematically  expressed.  But  it 
must  be  confessed  that  the  ether  itself,  as  he  defines  it, 
is  a  hypothetical  substance,  and  its  existence  lacks 
"  mechanical  confirmation."  Still,  this  is  not  an  in- 
superable objection,  for  all  scientific  induction  must 
start  with,  and  be  based  upon,  hypothesis.  The  ether 
is  a  scientific  necessity.  To  illustrate  :  In  the  mental 
conception  which  we  form  of  the  relations  of  bodies  in 
space,  and  of  the  parts  of  a  body  among  themselves, 
which  relations  we  symbolize  in  geometrical  figures, 
2 


1 8        UNITY  OF  NATURAL  PHENOMENA. 

we  are  obliged  to  have  recourse  to  a  hypothetical 
point.  In  geometry  solids  are  regarded  as  generated 
by  the  motion  of  surfaces,  surfaces  by  the  motion  of 
lines,  and  lines  of  points.  Beyond  this  we  are  not 
able  to  go.  By  an  analogous  train  of.  reasoning,  M. 
Saigey  builds  up  the  universe  out  of  the  ethereal  atom 
by  the  aid  of  motion.  Masses  are  made  of  compound 
particles  ;  the  particles  are  aggregations  of  molecules, 
and  the  molecules  may  be  resolved  into  atoms.  Be- 
hind this  veil  of  atoms  lies  the  Infinite.  Matter  is  a 
series  of  orderly  changes  from  the  immaterial,  becom- 
ing more  and  more  gross  until  recognized  by  the 
senses.*  Matter  is,  "at  bottom,  essentially  mystical 
and  transcendental."  f 

From  the  organic  forms  of  matter  M.  Saigey  passes 
to  living  beings,  to  plants  and  anim'als;  and  these  are 
likewise  brought  into  his  hypothesis.  The  primitive 
cell  of  the  plant,  as  well  as  the  embryonic  germ  of  the 
animal,  are  formed  out  of  the  materials  of  the  inorganic 
world.  In  both  a  series  of  motions  succeeds  each  other, 
according  to  a  fixed  order.  This  series  of  motions 
possesses  a  special  character,  it  is  true ;  but  their 
transformations  obey  the  laws  of  molecular  mechanics. 
The  origin  of  force,  the  nature  of  life,  human  person- 

*  Swedenborg,  Principia,  vol.  i.  chap.  ii. 
f  Fragments  of  Science,  p.  415. 


TRANSLATOR'S  INTRODUCTION.  19 

ality  —  questions  naturally  suggested  in  this  connec- 
tion —  are  considered  by  M.  Saigey  .as  entirely  foreign 
to  his  argument,  and  are,  therefore,  left  untouched. 
All  scientific  men  have  not  shared  the  forbearance 
of  our  author.  Emotions  and  ideas  display  outward 
phenomena  which  are  subject  to  the  laws  of  thermo- 
dynamics. Without  question  these  phenomena  are 
legitimate  subject  of  scientific  inquiry.  Some  time 
ago  a  series  of  experiments  was  published,  showing 
that  the  operations  of  the  mental  and  emotional  facul- 
ties are  accompanied  by  a  change  of  temperature  in 
the  brain.  The  greatness  of  an  idea  and  the  strength 
of  an  emotion  may  *peradventure  be  measured,  and 
their  mechanical  equivalent  determined.  Is  it  a  logi- 
cal inference  from  this  that  mind  is  a  quality  of  nerve 
tissue  ?  and  does  science  lay  us  under  any  obligations 
to  accept  the  dogmas  of  a  school  of  philosophy  which 
teaches  that  growth,  development,  and  human  progress 
are  results  of  self-determining  processes,  inherent  in 
the  very  nature  of  things  ?  There  is,  as  there  should 
be,  a  spirit  of  fearless  inquiry  abroad,  which  will  not 
stop  at  prescribed  bounds.  Unhappily  it  is  accom- 
panied by  a  spirit  of  irreverence,  for  which  a  New- 
ton or  a  Kepler  would  have  blushed.  The  scientific 
method  of  arriving  at  truth  may  be  the  most  exact  and 
satisfactory  one,  but  it  is  not  the  only  one.  The  fun- 


2O        UNITY  OF  NATURAL  PHENOMENA. 

damental  facts  of  revelation,  confirmed  by  the  methods 
of  a  spiritual  science,  rest  upon  proofs  as  sure  and 
convincing,  to  say  the  least,  as  any  established  by 
natural  science.  Between  these  two  methods  the 
utmost  harmony  may  and  ought  to  exist.  In  a  recent 
article  in  the  Contemporary  Review,  Dr.  Carpenter 
expresses  his  opinion  that  science  points  to  the  origi- 
nation of  all  power  in  Mind ;  and,  further,  that  there 
are  satisfactory  grounds  for  the  belief  that  the  phe- 
nomena of  the  material  'universe  are  the  expressions 
of  a  Mind  and  Will,  of  which  man's  is  the  finite  proto- 
type. To  admit  this  will  be  to  admit  the  existence  of 
the  supernatural,  always  working  in  and  through  the 

• 

natural.  Force  ceases  to  be  a  blind  attribute  of  mat- 
ter, and  becomes  a  living,  active  principle,  spiritual  in 
its  character. 

I  cannot  forbear  quoting  here  the  sublime  language 
of  one  who  may  rightfully  be  called  the  greatest  of 
living  naturalists,  one  who,  as  there  is  recent  ground 
for  believing,  has  thus  far  withstood  the  current  of  the 
Darwinian  theories  with  a  firmness  and  stability  like 
that  of  his  native  Alps. 

"  The  combination  in  time  and  space  of  all  these 
thoughtful  conceptions  (just  recapitulated),  exhibits 
not  only  thought,  it  shows  premeditation,  power,  wis- 
dom, greatness,  prescience,  omniscience,  providence. 


TRANSLATORS    INTRODUCTION,  21 

In  one  word,  all  these  facts  in  their  natural  connec- 
tion proclaim  aloud  the  one  God,  whom  man  may 
know,  adore,  and  love  ;  and  Natural  History  must,  in 
good  time,  become  the  analysis  of  the  thoughts  of  the 
Creator  of  the  universe,  as  manifested  in  the  animal 
and  vegetable  kingdoms."  * 

THOS.  FREEMAN  MOSES. 

URBANA  UNIVERSITY,  March  2,  1873. 

*  Agassiz,  Essay  on  Classification,  p.  135. 


AUTHOR'S    INTRODUCTION. 


THAT  heat  and  mechanical  force  are  mutually  equiv- 
alent is  a  fact  familiar  to  all  who  have  interested  them- 
selves in  the  progress  of  science.  Everywhere  we 
see  heat  converting  itself  into  force,  and  force  into 
heat.  In  the  steam  engine,  for  example,  the  heat 
disengaged  by  the  combustion  of  the  coal  is  turned 
into  the  labor  produced  by  the  shaft  of  the  engine. 
On  the  other  hand,  if  you  turn  a  wheel  in  a  body  of 
water,  the  water  becomes  warm ;  if  you  rub  together 
two  blocks  of  ice,  the  ice  melts.  All  around  .us,  in  the 
work  of  every-day  life,  we  see  a  certain  quantity  of 
heat  disappearing  at  the  same  time  that  a  certain 
amount  of  force  is  produced;  and  the  converse  is 
equally  well  known  from  the  most  familiar  facts.  Sim- 
ple as  this  notion  appears  to  us,  now  that  it  has  be- 
come a  part  of  our  current  ideas,  its  discovery  is, 
nevertheless,  the  principal  achievement  of  modern 
science. 

23 


24         UNITY  OF  NATURAL  PHENOMENA. 

The  works  of  Mr.  Joule,  the  eminent  philosopher 
of  Manchester,  those  of  Mr.  Jules-Robert  Meyer,  of 
Heilbronn,  of  Hirn,  the  Colmar  engineer,  after  hav- 
ing determined  the  conditions  of  the  convertibility 
existing  between  heat  and  mechanical  power,  have 
fully  brought  to  light '  the  principle  itself,  as  well  as 
the  reason  of  this  convertibility.  By  force  is  meant 
the  displacement  of  a  body.  Now,  heat,  as  every  one 
will  at  this  day  admit,  is  a  molecular  movement,  a  dis- 
placement of  molecules :  is  it  not  perfectly  natural,  then, 
that  these  two  phenomena  should  replace  each  other, 
according  to  a  fixed  relation,  and  that  between  these 
two  kinds  of  motion  there  should  exist  a  ready  con- 
vertibility governed  by  the  common  laws  of  me- 
chanics ? 

From  the  moment  of  the  introduction  of  this  pre- 
cise and  well-defined  idea  into  science,  every  branch 
of  physics  has  undergone,  in  some  degree,  a  renova- 
tion. Upon  many  questions  the  new  theory  has 
thrown  a  direct  light  ;  upon  others  it  has  furnished 
many  luminous  hints,  and  been  the  incentive  to  use- 
ful research.  Around  undisputed  facts  brought  to 
light  by  the  study  of  heat,  other  facts,  less  well  es- 
tablished, have  ranged  themselves,  then  ingenious 
conjectures,  and  from  this  impulse  of  ideas  has 
sprung  up  a  new  conception  of  nature,  which  has 


AUTHORS    INTRODUCTION.  2$ 

already  engaged  the  attention  of  many  scientific 
minds. 

In  turning  our  attention  to  this  new  way  of  view- 
ing natural  phenomena,  we  find  it,  at  the  outset,  a 
difficult  one  to  define. 

The  unity  of  physical  forces,  —  such  is  the  general 
formula  embracing  the  various  considerations,  of 
which  we  shall  attempt  a  rapid  review. 

In  the  system  before  us  all  the  forces  of  nature  are 
traceable  to  the  same  principle,  and  are  mutually  con- 
vertible under  certain  fixed  laws,  which  are  none  other 
tha.n  the  laws  of  mechanics.  Such  is  a  rude  and  gen- 
eral statement  of  the  new  theory,  a  statement  accept- 
ed by  different  scientific  minds,  not  without  certain 
restrictions.  Those  even  who  are  almost  agreed  as  to 
the  principle  itself  differ  when  it  becomes  necessary 
to  deduce  .certain  consequences  on  the  subject  of  the 
condition  of  matter  and  the  constitution  of  the  globe. 
It  is  here  that  we  meet  with  our  first  difficulty.  We 
shall  not  presume  to  set  forth,  in  subjects  so  impor- 
tant, a  collection  of  opinions  which  are  merely  person- 
al ;  nor,  on  the  other  hand,  may  we  venture  to  say,  that 
even  among  the  partisans  of  this  new  theory  has 
there  been  harmony  sufficient  to  establish  a  true 
scientific  system. 

In  undertaking  the  study  of  the  equivalence  of  heat 


26        UNITY  OF  NATURAL  PHENOMENA. 

and  motion  we  readily  find  some  useful  guides.  Com- 
plete treatises  upon  this  subject  already  exist,  and  he 
who  wishes  to  examine  its  leading  points  in'va  precise 
and  substantial  form  may  refer  to  the  excellent  lectures 
of  Mr.  Verdet,  published  in  the  Memoirs  of  the  Chemi- 
cal Society  of  Paris,  under  the  title  of  Expose  de  la 
Theorie  Mechanique  de  la  Chaleur.  In  examining  the 
unity  of  the  physical  forces,  however,  we  have  no  such 
aid  as  the  above.  It  would,  therefore,  seem  opportune 
at  this  time  to  give  some  definite  outline  to  ideas 
which  have  hitherto  remained  vague  and  ill  defined. 
We  have  already  made  an  attempt  in  this  direction 
in  a  number  of  articles  recently  published  in  the  Revue 
des  deux  Mondes,  and  which  form  the  substance  of  the 
Essay  now  presented  to  the  public.  It  will  be  grati- 
fying to  us  if  our  attempt  shall  call  forth  new  light 
upon  the  correlation  of  natural  phenomena,  and  if 
our  Essay  shall  hasten  the  publication  of  some  im- 
portant work  on  this  subject. 

In  1864,  Father  Secchi,  director  of  the  observatory 
of  the  Roman  College,  published  an  interesting  vol- 
ume, L'Unita  delle  forze  fisiche,  saggio  di  filosofia 
naturale.  Father  Secchi  cordially  adopted  the  idea 
that  the  physical  forces  are  all  traceable  to  one  and 
the  same  principle.  The  study  of  astronomical  phe- 
nomena has  itself  furnished  the  grounds  for  this  opin- 


AUTHOR'S  INTRODUCTION.  27 

ion.  In  reflecting  upon  the  force  of  gravity,  which 
gives  motion  to  the  heavenly  bodies,  he  was  not  ac- 
customed to  regard  it  as  an  elementary  principle,  but 
traced  it  back  to  a  still  more  general  law,  of  which 
this  force  is  only  a  consequence.  '  His  work  contains 
novel  and  original  suggestions  upon  this  subject.  At 
the  same  time  this  book  has  the  character  of  a  compen- 
dium of  physical  science.  It  reviews  in  a  summary 
manner  the  facts  which  to-day  compose  the  resources 
of  science  ;  only  accidentally  and  at  intervals  does  he 
touch  upon  the  general  principles  which  these  facts 
suggest.  We  do  not  find  here  any  theory  fully  set 
forth,  by  which  the  forces  of  nature  may  be  traced 
back  to  their  unity. 

We  might  mention  a  still  older  work,  that  of  M. 
de  Boucheporn,  published  in  1853,  under  the  title  of 
Principe  general  de  la  Philosophic  naturelle.  It  is  a 
work  compiled  with  care  and  zeal  —  one  of  those 
books  in  which  a  man  condenses  the  thought  of  a  life- 
time. M.  de  Boucheporn  seizes  with  boldness  upon 
the  synthesis  of  natural  phenomena.  He  recoils  be- 
fore no  difficulties,  he  meets  face  to  face  every  obsta- 
cle. Herein  lies  the  merit,  as  well  as  the  defect, 
of  his  work.  M.  de  Boucheporn  trusts  himself  too 
hastily  and  too  entirely  to  what  are  mere  guesses.  It 
is  wonderfuj  to  observe  how  a  conjecture  becomes  a 


28        UNITY  OF  NATURAL  PHENOMENA. 

certainty  with  him  as  soon  as  he  can  make  use  of  it 
in  accounting  for  certain  facts.  It  is  equally  a  won- 
der to  see  how  supple  facts  become  in  his  hands,  and 
how  readily  they  adapt  themselves  to  the-  demonstra- 
tions which  he  exacts  of  them.  Let  us  add  that  at 
the  time  when  M.  de  Boucheporn  published  the  Prin- 
cipe general  de  la  PhilosopJiie  naturelle,  the  new  theory 
of  heat  had  not  assumed  a  definite  position  in  science; 
if  was  but  just  being  evolved,  and  its  results  were  but 
poorly  comprehended,  and  the  author,  while  he  did 
not  ignore  them,  yet  derived  but  little  benefit  there- 
from. His  book,  too,  while  it  remains  full  of  interest 
in  what  relates  to  astronomy,  has  lost  much  of  its 
value  in  the  part  treating  of  the  laws  of  physics,  prop- 
erly so  called.  At  the  same  time  the  moment  we  set 
out  from  the  facts  revealed  by  the  study  of  heat,  the 
general  theory  which  we  wish  to  develop  can  hardly 
be  presented  as  otherwise  than  hypothesis.  As  we 
just  now  remarked,  a  serious  difficulty  presents  itself 
when  we  try  to  bring  under  a  precise  definition  that 
new  conception  of  nature  to  which  recent  investiga- 
tions have  given  rise.  In  what  language  shall  we  pre- 
sent it  in  order  that  it  may  not  appear  rash  to  some, 
to  others  chimerical,  and  to  many  useless  ?  Within 
what  bounds  must  we  retain  it,  that  we  may  not  seem 
to  overstep  the  facts  ?  May  we  be  permitted  to  adopt 


AUTHOR'S  INTRODUCTION.  29 

the   following  plan,  not  indeed  as  the  wisest,  but  as 
likely  to  throw  the  most  light  upon  the  subject  ? 

We  shall  begin  by  setting  forth  in  its  entirety,  and 
in  all  its  simplicity,  this  grand  hypothesis  which  we 
have  designated  under  the  name  of  the  Unity  of  Phys- 
ical Forces,  and  we  shall  try  to  demonstrate  its  im- 
mediate consequences.  We  shall  not  occupy  ourselves 
at  the  outset  with  bringing  forward  proofs  to  establish 
this  opinion. 

It  is  only,  in  conclusion,  that  we  shall  endeavor  to 
indicate  on  what  grounds  the  hypothesis  rests,  and 
the  restrictions  and  modifications  will  gradually  pre- 
sent themselves.  In  this  presentation  of  proofs  it  can^ 
easily  be  seen  how  much  belongs  to  experience,  how 
much  to  imagination  ;  what  can  be  believed  without 
scruple,  and  what  must  be  the  subject  of.  doubt  until 
further  information. 

With  this  understanding  at  the  outset,  we  beg  leave 
to  sketch  our  hypothesis  in  all  its  force,  without  being 
obliged  to  weaken  it,  as  we  proceed,  with  restrictive 
suggestions. 


THE 


UNITY  OF  NATURAL  PHENOMENA, 


CHAPTER   I. 
THE  GENERAL  HYPOTHESIS. 

I. 

Atoms  and  Motion.  —  Physical  Phenomena  may  be 
reduced  to  a  single  Principle,  and  considered  as  the 
Effects  of  Motion. 

THAT  matter  exists  throughout  the  universe  in  an 
unvarying  quantity  is  now  an  undisputed  fact,  and  one 
beyond  the  reach  of  controversy.  Never  is  it  created 
anew,  never  destroyed  ;  it  simply  passes  through 
transformations.  The  progress  made  by  chemistry 
in  the  beginning  of  this  century  set  forth  this  truth 
in  all  its  clearness,  and  made  it,  in  a  manner,  palpable. 

What  are,  in  fact,  the  properties  of  matter  ?  First, 
impenetrability,  as  implied  in  its  definition,  a  portion 

31 


32         UNITY  OF  NATURAL  PHENOMENA. 

of  matter  being  that  which  occupies  a  share  of  space 
to  the  exclusion  of  any  other  portion  ;  second,  inertia, 
it  being  the  principal  result  of  human  experiment,  and 
the  foundation,  indeed,  of  mechanics,  that  matter  is 
set  in  motion  only  when  it  receives  an  impression,  and 
loses  its  motion  only  in  communicating  it. 

We  can  say  the  same  of  motion  that  we  just  now 
said  of  matter  —  it  is  neither  created  nor  destroyed; 
'its  quantity  is  invariable.  With  motion,  as  with  mat- 
ter, it  is  only  a  question  of  transformation. 

Here  the  idea  of  Force  claims  our  attention.  What 
is  force  in  the  language  of  physics  and  mechanics  ? 
It  is  a  cause  of  motion  ;  but  what  idea  does  this  con- 
vey to  us  ?  The  cause  of  a  motion  is  another  motion. 
We  will  dispense,  then,  if  it  is  possible,  with  this  idea 
of  force,  or  rather,  —  for  it  is  necessary  to  employ  cus- 
tomary terms  in  order  to  be  intelligible,  —  we  will  un- 
derstand by  force  whatever  causes  one  motion  to  give 
place  to  another  motion. 

If  now,  leaving  these  abstract  considerations  and 
entering  the  domain  of  facts,  we  ask  what  are  the 
physical  phenomena  which  appeal  to  our  senses,  heat, 
light,  electricity,  magnetism,  we  find  it  demonstrated 
that  heat  is  one  kind  of  motion,  and  that  light  is  an- 
other, and  we  are  made  to  perceive  that  it  is  the  same 
with  electricity  and  magnetism.  There  is  nothing, 


THE   GENERAL    HYPOTHESIS.  33 

then,  which  need  surprise  us  if  one  of  these  motions 
should  engender  the  other  ;  that  heat  should  be  trans- 
formed into  electricity,  and  electricity  into  light. 
When  the  solar  rays  draw  up  water  from  the  surface 
of  rivers  and  lakes,  when  clouds  are  formed,  when 
these  clouds  become  charged  with  electricity  and  the 
lightning  flashes,  and  when  the  watery  vapor  falls  in 
rain  to  the  ground,  we  see  under  these  various  ap- 
pearances only  a  series  of  successive  motions.  Not 
only  do  we  find,  at  the  end  of  the  phenomenon,  the 
whole  quantity  of  water  employed  in  it,  but  the  mind 
follows  easily  its  various  modifications  from  its  first 
motion.  Now,  it  will  be  understood  that  these  trans- 
formations take  place  according  to  certain  fixed  rela- 
tions. If  the  various  kinds  of  motion  be  measured 
according  to  certain  established  units,  all  these  units 
are  reducible  to  a  common  scale ;  a  unit  of  heat  cor- 
responds always  to  425  kilogrammetres,*  to  425 
units  of  mechanical  power ;  there  is  an  analogous 
relation  between  the  electric  unit  and  the  heat  unit, 
and  so  on. 

If,  now,  we  touch  upon  another  order  of  facts,  if  we 
consider  another  group  of  forces,  the  cohesion  which 

*  The  kilogrammetre  is  the  power  represented  by  a  kilogramme 
(2^  pounds  nearly)  elevated  to  the  height  of  a  metre  (about  40 
inches). 

3 


34         UNITY  OF  NATURAL  PHENOMENA. 

keeps  bodies  either  in  a  solid  or  liquid  state,  the 
chemical  affinity  which  attracts  molecules  of  differ- 
ent kinds,  that  force  of  gravity,  in  a  word,  by  virtue  of 
which  bodies  tend  to  move  towards  each  other,  the 
new  theory  enables  us  to  perceive  still  farther  how  the 
play  of  all  these  forces  is  reducible  to  certain  communi- 
cations of  motion.  Here  is,.for  example,  a  piece  of  lead, 
whose  molecules  adhere  in  such  a  manner  as  to  form 
a  solid  block.  I  know  that  in  heating  them,  in  com- 
municating to  them  a  certain  kind  of  motion,  I  shall 
destroy  the  cohesion  by  virtue  of  which  the  block  re- 
mains solid,  and  I  shall  subject  it  to  a  different  cohe- 
sion, which  belongs  to  the  liquid  state.  Heating  it  still 
more,  and  thus  augmenting  the  amount  of  communi- 
cated motion,  I  shall  destroy  even  this  kind  of  cohe- 
sion, and  reduce  the  metal  to  vapor.  Hence  may  we 
not  suppose  that  the  cohesion  which  held  together 
the  molecules  of  the  lead  was  a  motion  relatively  of 
those  molecules  ?  Whatever  we  destroy  by  a  motion 
must  he  itself  a  motion.  Cohesion,  we  say,  proceeds 
from  a  relative  motion.  Do  we  not  see  it  in  some 
cases  result  simply  from  a  common  velocity  imparted 
to  neighboring  molecules. 

When  a  jet  of  water,  for  example,  escapes  from  an 
orifice  under  strong  pressure,  does  it  not  assume  a 
solid  form,  and  is  there  not  a  kind  of  cohesion  result- 


THE    GENERAL    HYPOTHESIS.  35 

ing  from  the  fact  that  all  its  molecules  in  the  same 
plane  move  onward  with  an  equal  velocity  ?  The 
familiar  example  we  have  cited  will  not  be  regarded 
as  a  demonstration  of  facts.  At  present  we  do  not 
endeavor  to  crowd  together  phenomena  ;  we  shall 
strive  only  to  show  in  what  manner  the  new  theory 
presents  itself  to  our  view.  We  would  not  discuss  its 
revelations.  We  seek  only  to  present  them  to  view. 

In  regard  to  chemical  affinity,  we  shall  only  be  al- 
lowed to  say  a  word  here,  for  in  many  respects  its 
action  is  similar  to  that  of  cohesion,  and  somewhat 
analogous  to  that  of  gravity.  When,  under  certain 
conditions,  particles  of  oxygen  and  carbon  meet,  they 
are  precipitated  upon  each  other  after  the  manner  of 
heavy  bodies,  and  when  they  are  combined  to  form 
the  oxide  of  carbon  or  carbonic  acid,  the  fixed  state 
which  they  enter  upon  may  be  compared  to  that  of 
planetary  bodies  which  revolve  about  each  other. 

What,  then,  is  gravity  ?  What  is  that  mysterious 
force  which  causes  two  bodies  to  attract  each  other 
in  the  direct  ratio  of  their  masses  and  the  inverse 
ratio  of  their  distance  ?  Two  bodies  attract  each 
other  !  Then  matter  is  not  inert !  Would  there  not 
appear  to  be  a  real  contradiction  between  the  two 
terms,  matter  and  inertia  ? 


36        UNITY  OF  NATURAL  PHENOMENA. 

The  question  is  one  well  worthy  our  close  attention 
and  examination. 

Here  are  two  molecules  of  matter.  Is  it  a  sound 
notion  to  imagine  them  as  setting  out  voluntarily  from 
a  state  of  repose  for  the  purpose  of  approaching  each 
other  again  ?  Strictly  speaking,  I  can  conceive  of 
this  being  the  case,  and  if  all  the  particles  'of  matter 
attract  each  other  by  virtue  of  a  hidden  force  which 
resides  in  them,  I  can  comprehend  without  difficulty 
the  vast  amount  of  motion  diffused  throughout  the 
universe ;  but  from  the  very  moment  that  I  cease  to 
speak  of  matter  as  inert,  I  am  obliged,  on  the  other 
hand,  to  say  that  it  is  active,  since  I  acknowledge  that 
it  encloses  a  principle  of  action.  Here  we  find  our- 
selves face  to  face  with  an  immense  difficulty;  and  it 
will  be  said,  doubtless,  that  every  scientific  man  since 
Newton  has  been  obliged  to  solve  it,  since  it  is  impos- 
sible to  leave  at  the  very  foundation  of  Science  two 
contradictory  assertions.  In  fact,  minds  habituated 
to  scientific  pursuits  know  that  it  is  necessary  to  seek 
outside  of  bodies  the  cause  by  which  they  tend  to- 
wards each  other ;  they  know  that  in  enunciating  the 
law  of  universal  gravitation,  they  regard  results,  and 
not  causes,  and  only  mean  that  things  take  place  as  if 
bodies  were  attracted  in  direct  ratio  of  their  mass, 
and  inverse  ratio  of  their  distance.  Such  is  the  res- 


THE    GENERAL    HYPOTHESIS.  37 

ervation  which  all  sensible  minds  have  made,  or  ought 
to  have  made,  more  or  less  explicitly. 

Now,  what  light  is  this  new  theory  going  to  throw 
upon  the  principle  of  gravity  ?  Here  is  the  answer. 
A  substance  to  which  the  name  of  ether  has  been 
given  is  diffused  throughout  the  entire  universe.  It 
envelops  bodies,  and  penetrates  into  their  interstices. 
The  existence  of  this  substance  is  deduced  from  a 
series  of  proofs,  among  which  luminous  phenomena 
hold  the  first  rank.  Ether  is  composed  of  atoms 
which  impinge  upon  each  other  and  upon  neighboring 
bodies.  It  forms,  in  this  way,  a  universal  medium, 
which  exerts  a  constant  pressure  upon  the  molecules 
of  ordinary  matter.  The  new  theory  accounts  for  the 
reactions  which  are  produced  between  the  ethereal 
atoms  and  the  material  molecules ;  it  proves  that  these 
reactions  are  such  that  the  material  molecules  must 
tend  towards  each  other  precisely  according  to  the  con- 
ditions which  the  law  of  gravity  also  observes.  We 
shall  attempt  farther  on  to  give  an  idea  of  this  ingen- 
ious demonstration.  For  the  present  we  leave  aside  all 
the  proofs,  and  only  declare  results.  Every  one  will 
understand  the  importance  of  the  point  to  which  we 
have  just  arrived.  It  becomes  evident  that  bodies  do 
not  owe  their  gravity  to  an  intrinsic  force,  but  to  the 
pressure  of  the  medium  in  which  they  are  immersed. 


38        UNITY  OF  NATURAL  PHENOMENA. 

The  motion  of  heavy  bodies  would  no  longer  appear 
to  us  other  than  as  a  transformation  of  the  ethereal 
motions,  and  gravity,  henceforth,  enters  into  that  ma- 
jestic unity  to  which  we  have  conducted  all  physical 
forces. 

Thus  heat,  light,  electricity,  magnetism,  cohesion, 
chemical  affinity,  gravity,  are  all  resolved  into  the 
idea  of  motion.  All  these  motions  may  be  converted 
into  each  other  according  to  fixed  relations,  some  of 
which  are  known,  but  by  far  the  greatest  number  of 
which  is,  as  yet,  undetermined. 

Let  us  see  if  the  idea  of  matter  will  not  henceforth 
be  rendered  more  simple  and  clear.  At  the  founda- 
tion of  our  system  we  have  the  atom  of  ether.  But 
is  there,  —  we  supposed  it  just  now  for  the  sake  of 
making  ourselves  more  easily  understood,  —  is  there 
really  an  ether,  and  an  ordinary  matter,  differing  from 
ether  in  •  its  essence  ?  To  speak  more  clearly,  are 
there  two  kinds  of  matter?  We  can  hardly  conceive 
it,  now  that  we  have  resolved  everything  into  motion. 
In  what  respect  would  these  two  kinds  of  matter  dif- 
fer ?  Would  not  the  one  be  subject  to  the  same  laws 
of  motion  as  the  other.  Can  there  be  two  systems  of 
mechanics  ?  Certainly  not ;  since  there  is  but  one 
law  for  motion,  there  can  be  but  a  single  essence  for 
matter,  and  the  molecules  of  ordinary  matter  must 


THE   GENERAL   HYPOTHESIS.  39 

appear  to  us  as  aggregates  of  ethereal  atoms.  It  is 
under  this  form  that  we  shall  represent  the  elemen- 
tary particles  of  simple  bodies,  of  iron,  lead,  oxygen, 
carbon.  The  molecules  of  these  bodies  do  not  differ 
in  their  substance,  but  simply  in  the  interior  arrange- 
ment of  the  ethereal  atoms  which  compose  them. 

Because  iron,  lead,  oxygen,  carbon,  chemically  unite 
in  different  combinations,  must  we  suspect  in  them 
some  difference  in  substance  ?  Upon  what  would  this 
difference  depend,  since  chemical  affinity  itself  pre- 
sents to  us  only  the  idea  of  motion  ? 


II. 


The  Hypothesis  of  the  Unity  of  Natural  Phenomena 
in  its  Relation  to  Science. 

FROM  the  point  now  reached,  we  may  consider,  in 
all  its  bearings,  the  hypothesis  whose  principal  fea- 
tures we  have  just  traced.  If  it  be  admitted  in  its 
entire  force,  natural  phenomena  present  themselves 
under  a  form  so  simple  as  to  surprise  the  mind  at 
once  with  wonder  and  awe.  The  physical  world  is 
composed  of  atoms  of  one  kind.  By  virtue  of  a  mo- 
tion received  and  communicated  to  each  other  by 
these  atoms,  they  become  so  grouped  and  inter- 


4O         UNITY  OF  NATURAL  PHENOMENA. 

mingled  as  to  form  simple  molecules,  compound  mole- 
cules, gaseous,  liquid,  and  solid  bodies.  It  is  to  one 
and  the  same  cause, — namely,  ^to  motions  received  and 
converted  into  others,  —  that. we  must  attribute  mo- 
lecular aggregations  in  the  realm  of  the  infinitely  small, 
and  in  that  of  the  infinitely  large  the  gravitation  of 
the  heavenly  bodies.  It  is  this  motion  of  a  fixed  na- 
ture which,  either  in  bodies  or  outside  of  them,  con- 
stitutes the  phenomenon  we  call  heat ;  it  is  the  same 
motion  which,  under  another  peculiar  form,  consti- 
tutes light,  under  another  electricity,  and  so  on. 

The  atom  and  motion  !     Behold  the  universe  ! 

Upon  this  basis  will  the  mathematician  be  able  to 
construct  his  calculations.  While  applying  his  equa- 
tions to  a  medium  composed  of  uniform  atoms,  and 
seeking  all  the  motions  which  may  be  produced,  and 
all  the  combinations  that  may  spring  from  these  mo- 
tions, he  will  come  again  to  the  recognized  phenomena 
of  physical  science,  the  laws  of  the  planetary  circu- 
lation, of  the  propagation  of  sound,  of  luminous  undu- 
lations. Entered  upon  this  path,  he  will  determine 
by  means  of  the  analogies  which  such  a  study  will  sug- 
gest, in  addition  to  motions  known  and  recognized, 
motions  which  appear  probable.  He  will  here  find 
again,  doubtless,  the  laws  of  matter  studied  already ; 
he  will  here  find,  perhaps,  properties  towards  which 


THE   GENERAL   HYPOTHESIS.  4! 

the  attention  of  man  has  never  been  directed.  How 
many  important  laws  thus  reign  around  us  without 
our  even  suspecting  it !  How  long  men  lived  with- 
out a  suspicion  of  the  electric  phenomena  whose  action 
encircles  them !  What  unexpected  revelations  may 
spring  up  from  this  study  of  nature  from  a  new  point 
of  view ! 

Here  let  us  speak  only  of  the  obscurities  which  the 
new  hypothesis  has  already  dispelled,  and  let  us  leave 
to  the  future  the  task  of  justifying  the  hopes  to  which 
it  has  given  rise.  By  means  of  the  bond  which  it  es- 
tablishes between  all  natural  phenomena,  our  minds 
are  accustomed  to  seek,  in  every  fact,  through  the 
transformations  which  formerly  obscured  our  vision, 
its  immediate  origin  and  its  direct  result. 

When  we  see  a  steam  engine  raise  a  weight,  or 
overcome  a  resistance,  we  think  at  once  of  the  coal 
burning  in  the  furnace,  whose  combustion  effects  the 
work  of  the  machinery.  But  where  does  the  coal  get 
this  power  which  we  know  how  to  utilize  ?  It  is  the 
product  of  a  long-continued  work  of  the  sun,  stored  up 
in  fossil  vegetables.  Thus  all  facts  are  brought,  as  it 
were,  to  a  common  standard,  and  we  become  accus- 
tomed to  look  always  for  a  due  proportion  between 
cause  and  effect. 

To  give  a  familiar  form  to  thought,  may  we  here 


42         UNITY  OF  NATURAL  PHENOMENA. 

cite  an  anecdote  ?  We  will  borrow  it  from  Father 
Secchi,  who  relates  it  in  his  work  upon  the  unity  of 
physical  forces.  There  was,  in  1855,  at  the  Universal 
Exhibition  in  Paris,  a  huge  bell,  of  enormous  weight ; 
it  was  held  up  by  a  system  of  props  so  ingenious  that  a 
single  man  was  able  to  keep  it  in  motion ;  only  the 
tongue  had  been  removed,  without  doubt  out  of  regard 
for  the  ears  of  visitors.  The  man  who  exhibited  the 
bell  easily  kept  it  swinging,  and  the  spectators  admired 
the  facility  with  which  he  made  this  formidable  engine 
move.  An  ecclesiastic,  an  educated  and  intelligent 
man,  —  we  may  suspect  that  it  was  Father  Secchi 
himself,  —  approached  the  exhibitor,  and  said  to 
him, — 

"  Your  system  of  supports  is  very  well  contrived ; 
it  permits  you  to  set  this  huge  mass  in  motion  with 
extreme  facility ;  but  would  it  be  the  same  if  the  bell 
had  its  clapper,  and  if  it  struck  ? " 

Those  standing  by  doubtless  did  not  understand  the 
thought  of  the  jocose  ecclesiastic. 

The  fact  really  was,  if  the  bell  had  been  forced  to 
give  out  sounds,  —  that  is  to  say,  to  make  the  air  vibrate 
strongly,  —  he  would  have  failed  with  his  best  efforts  to 
find  the  necessary  strength  to  produce  such  a  vibra- 
tion. However  perfect  had  been  the  mechanism  of 
the  support,  this  strength  would  have  been  borrowed 


THE   GENERAL   HYPOTHESIS.  43 

from  the  arm  which  pulled  the  rope.  When  a  bell 
vibrates,  it  is  the  labor  of  the  bell-ringer  which  is 
turned  into  sound.  To  remove  the  tongue  —  that  is  to 
say,  to  prevent  the  sound — is  to  render  the  task  easy 
to  the  ringer. 

As  is  the  cause,  so  is  the  effect.  We  find  ourselves 
placed  at  this  point  of  view  whenever  we  attempt  to 
recall,  briefly,  the  main  facts  upon  which  rests  the 
unity  of  physical  forces.  Before  entering  upon  the 
examination  of  this,  we  desire  to  reply  to  two  ques- 
tions which  arise  about  the  hypothesis  we  are  devel- 
oping. 

Is  this  hypothesis  a  useful  one  ? 

Is  this  hypothesis  really  new  ? 

Firstly,  is  it  useful  ?  The  great  advancements 
made  by  modern,  science- are  due  to  experiment  and 
observation.  Non  fingo  hypotheses,  wrote  Newton  as 
preface  to  his  works.  Nullius  in  verba,  proclaimed 
the  escutcheon  of  the"  Royal  Society  of  London.  Pro- 
vando  e  riprovando,  was  likewise  the  inscription  upon 
the  shield  of  the  Florentine  Academy,  founded  by 
Galileo.  Certain  it  is  that  modern  physical  science 
has  done  away  with  examining  phenomena  themselves, 
independently  of  their  supposed  causes,  by  subjecting 
them  always  to  exact  instrumental  measurements.  We 
can  to-day  appreciate  with  the  utmost  exactness  the 


44        UNITY  OF  NATURAL  PHENOMENA. 

thousandth  part  of  a  millimetre  (a  millimetre  —  .039 
inch),  the  ten  thousandth  part  of  a  second,  and  we  are 
not  likely  to  give  over  the  researches  which  such  means 
of  investigation  enable  us  to  undertake.  Surely  the 
experimental  method,  which  has  given  birth  to  such 
brilliant  results,  is  not  likely  to  perish,  and  it  is  always 
of  the  vernier  of  the  physicist,  the  scales  of  the  chem- 
ist, the  scalpel  of  the  physician,  the  telescope  of  the 
astronomer,  that  we  must  ask  for  sure  information  in 
regard  to  Nature. 

Is  this  to  say,  nevertheless,  that,  while  this,  incessant 
work  of  research  is  pushed  in  all  directions,  we  may 
not  attempt  to  group  together  facts  already  discovered, 
in  such  a*  manner  as  to  rise  to  more  and  more  general 
laws  ?  Vain  would  be  the  attempt  to  combat  this  ten- 
dency of  the  human  mind.  It  is  easy  to  say  that  one 
must  concern  himself  only  with  proven  facts,  and 
leave  the  rest  to  dreamers ;  but  it  is  not  so  easy  to 
keep  to  this  programme.  Every  one  is  irresistibly  led 
to  form  for  himself  an  idea  of  the  universe  as  a  whole, 
be  it  correct  or  not.  Among  men  who  make  real 
progress  in  science,  those  even  who  appear  most  ab- 
sorbed in  searching  after  particular  facts,  those  who 
confine  themselves  to  the  patient  investigation  of  par- 
ticular phenomena,  certainly  have  their  general  theo- 
ries, which  they  forbear,  perhaps,  to  communicate  to 


THE    GENERAL    HYPOTHESIS.  45 

the  public,  but  which  guide  them  in  their  labors, 
which  induce  them  to  attack  one  question  rather  than 
another,  which,  true  or  false,  suggest  new  ideas  to 
them,  and  classify  their  difficulties. 

Far  above  all  the  theories  which  have  thus  guided 
men  of  science,  now  rises  this  grand  conception  of  the 
unity  of  the  physical  forces.  It  is  only  an  hypothesis, 
but  it  offers  itself  with  guaranties  sufficiently  sure  to 
necessitate  a  kind  of  revision  of  science  as  a  whole. 
It  will  illuminate  with  new  light  facts  already  known, 
trace  out  a  new  path  for  researches  in  questions  hith- 
erto beset  with  difficulty  and  doubts,  and  point  out  in 
what  direction  it  is  necessary  first  to  question  Nature. 
Were  the  hypothesis  false,  experience  would  know 
how  to  profit  by  it.  • 

But,  it  will  be  said,'  is  it  not  to  be  feared  that,  led 
away  by  this  seductive  theory,  many  observers  will 
come  to  pay  but  little  attention  to  facts,  and  strive  to 
force  them  into  the  outline  they  have  sketched  in  ad- 
vance, and  thus  unwittingly  falsify  the  results  of  their 
experiments  before  presenting  them  to  the  public  ? 
This  will  doubtless  happen  —  it  has  already  happened  ; 
but  it  is  not  a  very  serious  evil, 'for  science  is  well 
enough  armed  against  such  a  danger,  and  erroneous 
assertions  cannot  long  resist  its  control. 

But,  it  will  be  again  objected,  scientific  men  are  not 


46        UNITY  OF  NATURAL  PHENOMENA. 

the  only  ones  concerned  in  the  matter.  Your  hypoth- 
esis lays  hold  upon  philosophy.  Not  only  does  it 
comprise  all  physical  science,  but  it  also  enters  the 
domain  of  metaphysics.  Philosophers  will  doubtless 
adopt  it,  believing  that  they  hold  in  their  grasp  a 
scientific  truth,  and  they  will  find,  perhaps,  that  they 
embrace  only  a  chimera !  What  reply  do  you  make 
to  that  ?  The  metaphysicians  must  have  a  care  to 
keep  themselves  well  informed. 

Now,  is  this  veritably  a  new  hypothesis,  which  pre- 
sents the  physical  world  to  us  as  composed  of  uniform 
atoms  and  diverse  motions  ? 

Properly  speaking,  there  are  but  few  ideas  which 
can  be  brought  forward  as  entirely  new.  If  we  con- 
fine ourselves  to  mere  definitions  and  the  surface  of 
things,  we  shall  discover  the  theory  of  the  unity  of  the 
physical  forces  in  the  remotest  antiquity.  The  phi- 
losophers of  ancient  Greece  did  not  have  a  single  fact, 
scientifically  demonstrated,  at  their  disposal,  so  to 
speak,  and  in  this  state  of  things  they  formed  the 
most  simple  hypothesis  concerning  Nature.  They  had 
a  clear  field,  and  nothing  interfered  with  their  em- 
piricism ;  so  they  went  straight  to  the  most  general 
conceptions,  and  every  one  in  his  own  way  made  unity 
out  of  the  grand  total.  Thales  of  Miletus,  six  hun- 
dred years  before  our  era,  began  by  declaring  that 


THE   GENERAL    HYPOTHESIS.  47 

water  was  the  principle  of  all  things.  Fifty  years 
later  his  countryman,  Anaximene,  beheld  in  air  "  the 
uniform  and  primitive  element."  The  Eleatic  school, 
in  Magna  Grecia,  sought  elsewhere  the  universal  prin- 
ciple. "  Nothing  proceeds  from  nothing,  and  nothing 
can  change,"  said  Xenophanes  ;  "  everything  possess- 
es the  same  nature ; "  nevertheless  he  demanded,  in 
order  to  account  for  the  multiplicity  of  variable  sub- 
stances, two  elements,  water  and  the  earth.  About 
the  year  500,  Heraclitus  adopted  fire  as  the  unique 
principle  and  universal  agent.  "  The  world  is  neither 
the  work  of  gods  nor  of  men  ;  it  is  an  ever-living  fire, 
enkindling  itself  and  extinguishing  itself  according  to 
a  certain  order."  Here,  then,  are  four  elements  suc- 
cessively proclaimed  —  water,  air,  earth,  fire  ;  and 
by  a  kind  of  eclecticism,  they  came  to  be  admitted,  all 
four  at  once,,  into  the  composition  of  the  universe. 
Aristotle  accepted  these  four  elements,  and  for  long 
ages  after  him  they  served  as  the  basis  for  every  sys- 
tem of  nature.  During  the  eighteenth  century  the 
four  elements  were  still  admitted,  on  the  eve  of  the 
great  works  which  have  founded  modern  chemistry. 
Pursuing  this  general  progress  of  ideas,  we  en- 
counter the  Atomic  theory  itself  in  very  ancient 
times.  Leucippus,  an  Eleatic,  who  lived  five  hundred 
years  before  our  era,  conceived  the  universe  as  formed 


4o        UNITY  OF  NATURAL  PHENOMENA. 

of  a  vacuum,  and  a  real  substance,  the  last  division 
of  which  was  the  atom.  "  The  round  atoms,"  he  said, 
"have  the  property  of  motion.  Jt  is  the  combining 
and  separating  of  these  which  give  birth  to  things  and 
destroy  them.  All  physical  phenomena  are  deter- 
mined by  the  order  and  position  of  the  atoms,  and 
only  take  place  by  virtue  of  necessity."  Democritus 
of  Abdera,  a  Disciple  of  Leucippus,  developed  his 
doctrine.  He  attributed  to  atoms,  similar  to  each 
other,  original  properties,  impenetrability,  and  a  sort 
of  weight.  For  him  "  every  active  influence  or  every 
passive  impulse  is  a  motion  following  contact." 

He  distinguished  impulsive  (7zak[i6$)  and  the  move- 
ment of  reaction  (avtivvnia),  whence  results  the  circu- 
lar or  whirling  motion  (divrf).  In  this  consists  the  law 
of  necessity  (avctym])  pointed  out  by  Leucippus.  Epi- 
curus, the  Athenian,  adopted  the  views  of  Democritus, 
and  made  a  kind  of  atomic  theory.  He  gave  to  the 
atoms  a  hooked  form,  and  supposed  them  endowed 
with  an  oblique  motion  in  relation  to  each  other,  in 
order  that  they  might  be  able  to  grasp  each  other,  and 
form  bodies.  Such  is  the  system  of  which  Lucretius 
sang  in  his  magnificent  poem  of  Nature. 

But,  need  we  repeat  it  ?  the  conceptions  of  these 
philosophers,  of  these  poets,  were  purely  Utopian. 
Formed  outside  of  facts,  they  brought  no  light  into 


THE   GENERAL   HYPOTHESIS.  49 

the  domain  of  physical  science  ;  their  authors  could 
see  in  them  only  what  they  themselves  had  put  there, 
that  is,  the  caprice  of  their  imagination ;  thus  they  did 
not  possess  for  them  the  meaning  which  they  now 
have  for  us.  In  their  eyes  they  were  but  simple  for- 
mulae, which  they  little  cared  to  confront  with  the 
facts  of  Nature,  and  which  served  only  as  preambles 
to  their  systems  of  philosophy. 

What  we  say  of  the  ancients  wholly  applies  to  the 
middle  ages,  to  the  period  of  the  Renaissance,  to  the 
primitive  works  of  modern  times.  The  physical  sys- 
tem of  Descartes  has  scarcely  more  value  than  that 
of  Epicurus ;  the  same  fantasy,  the  same  vortices, 
the  same  hooked  atoms. 

The  great  men  who,  at  the  time  even  of  Descartes, 
inaugurated  the  remodelling  of  the  sciences,  concerned 
themselves  only  with  facts,  and  left  aside  hypotheses. 
Such  was  Kepler,  such  was  Galileo.  When  the  sec- 
ond generation  of  great  savans  came,  the  generation 
of  Newton,  of  Leibnitz,  of  Huyghens,  so  rich  was  the 
store  of  precise  information  that  a  general  hypothesis 
was  well  nigh  impossible.  Science  was  divided  into 
several  branches.  In  each  one  of  them  they  made 
one  or  more  particular  hypotheses  ;  but  it  was  a  long 
time  before  they  thought  to  include  in  one  general 
4 


5O        UNITY  OF  NATURAL  PHENOMENA. 

formula  the  numerous  and  exact  phenomena  which  a 
diligent  and  laborious  search  was  bringing  to  light. 

If,  now,  from  the  mere  examination  of  these  phe- 
nomena a  general  formula  arises,  if  a  system  springs 
up  spontaneously  from  the  study  of  observed  facts,  we 
may  pronounce  it  veritably  new,  even  if  its  formula 
should  be  ancient,  if  even  there  might  be  found  in 
Democritus  an  almost  complete  enunciation  of  it. 
The  originality  of  the  hypothesis  brought  forward  at 
this  time  consists  in  this,  that  it  has  the  support  of  a 
considerable  number  of  facts  ;  that  it  has  its  birth  in 
these  facts.  It  borrows  its  worth  from  the  facts  it 
embraces ;  it  becomes,  in  a  certain  manner,  a  fact  it- 
self. 


III. 


The  Difficulty  encountered  by  endeavoring  to  express 
.  new  Ideas  by  Means  of  Old  Terms. 

THE  theory  we  are  investigating  will  only  appear 
in  its  true  light  when  we  have  examined  some  of  the 
phenomena  upon  which  it  rests,  and  pointed  out  the 
new  aspect  which  it  gives  to  certain  portions  of 
science. 

We  have  no  intention,  as  may  be  thought,  of  giving 
a  course  of  lectures  on  Physics.  We  shall  only  be 


THE   GENERAL   HYPOTHESIS.  51 

able  to  touch  upon  certain  points,  to  throw  out  a  few 
hints. 

Do  not  ask  of  us  a  general  picture  of  Nature,  when 
we  only  seek  to  sketch  a  few  details  of  it ;  through 
these  partial  openings  may  doubtless  be  seen  what 
would  be  the  scope  of  the  work  which  we  do  not 
dream  of  undertaking. 

Furthermore,  we  shall  adopt,  in  our  cursory  survey  of 
natural  phenomena,  the  same  order  we  have  pursued 
in  our  summary  exposition  of  the  system.  We  shall 
speak  first  of  what  relates  to  light,  heat,  electricity ; 
we  shall  next  come  to  that  other  group  of  actions, 
chemical  affinity,  cohesion,  gravity,  the  principle  of 
which  current  prejudices  more  especially  locate  in  the 
very  bosom  of  the  molecules. 

Heat !  Electricity  !  Cohesion  !  Gravity  !  we  say. 
These  words  even  bring  us  to  make  a  declaration,  the 
advantage  of  which  will  accrue  to  us  during  the  whole 
course  of  this  essay. 

In  every  branch  of  physical  science,  we  just  now  said, 
particular  hypotheses  have  been  made.  They  have 
influenced  the  language  which  has  been  adopted  in  the 
various  branches  of  science.  In  many  cases  the  names 
given  to  the  phenomena,  the  classification  of  them 
even,  are  in  disagreement  with  the  new  theory. 

What  are  we  to  do  under  these  circumstances? 


52   •     UNITY  OF  NATURAL  PHENOMENA. 

* 

Undoubtedly  for  a  new  situation  there  is  needed  a  new 
language.  But  shall  we  create  here  this  new  language 
complete  in  all  parts  ?  We  have  many  other  difficul- 
ties to  encounter. 

Shall  we  have  recourse  to  paraphrases  in  order  to 
avoid  words  which  seem  to  contradict  the  idea  we  are 
unfolding  ?  We  should  run  a  great  risk  of  not  being 
understood. 

We  shall  continue,  then,  to  call  all  things  by  their 
customary  names  ;  if,  however,  this  nomenclature 
be  found  in  disagreement  with  .  our  fundamental 
idea,  we  beg  that  the  accident  may  be  kindly  attrib- 
uted to  the  state  of  transition  through  which  physical 
science  is  now  passing.  In  former  times  the  electri- 
cians admitted  the  existence  of  a  positive  and  a  nega- 
tive fluid.  They  recognized,  henceforth,  in  a  current 
a  positive  pole  and  a  negative  pole ;  we  shall  do  as 
they  have  done,  without  its  leading  to  material  conse- 
quences. When  a  body  is  heated  without  being  per- 
mitted to  expand,  it  absorbs,  in  order  to  acquire  a 
certain  degree  of  temperature,  a  determined  quantity 
of  heat,  and  if  it  is  heated  and  also  allowed  to  expand, 
it  requires,  to  arrive  to  the  same  temperature,  a  greater 
quantity  of  heat.  Physicists  have  given  to  the  excess 
of  heat  demanded  in  the  second  case  the  name  of  la- 
tent heat  of  dilatation.  We  may  continue  to  call  it 


THE    GENERAL   HYPOTHESIS.  53 

latent,  while  seeing  clearly  that  it  is  used  up'  in  pro- 
ducing the  mechanical  work  of  'dilatation. 

In  studying  the  molecular  actions,  there  have  al- 
ways been  recognized  attractive  forces  and  repulsive 
forces ;  we  may  do  the  same,  prejudging  nothing  as  to 
the  existence  of  these  forces. 

As  to  the  word  Force  itself,  we  preserve  it  for  want 
of  a  better  in  our  vocabulary.  Every  tirfle  a  motion 
appears  to  us  as  the  continuation  or  the  transmuta- 
tion of  another  motion,  we  can  do  without  the  idea  of 
force,  and  we  ought  tQ  reserve  this  notion  for  motions, 
the  origin  of  which  remains  entirely  concealed  from 
us.  We  shall  continue,  nevertheless,  as  we  have  done 
in  the  preceding  pages,  to  employ  the  word  force  in 
its  customary  sense.  We  shall  speak,  without  scruple, 
of  the  force  of  gravity  which  causes  a  stone  to  fall,  and 
of  the  force  of  cohesion  which  maintains  a  body  in 
the  solid  state,  at  the  same  time  supposing  that  the 
fall  of  the  stone  and  the  solidity  of  the  body  are  due 
only  to  movements  of  the  surrounding  medium. 

To  speak  truly,  the  inconvenience  we  here  point 
out  is  not  a  new  one,  and  these  difficulties  of  lan- 
guage are  well  known  in  physics.  As  in  each  of  the 

» 

parts,  of  this  science  different  hypotheses  have  been 
successively  made  for  the  purpose  of  grouping  and 
co-ordinating  the  phenomena,  so  physicists  have 


54        UNITY  OF  NATURAL  PHENOMENA. 

learned,  in  a  certain  measure,  to  withdraw  themselves 
from  the  empire  of  words,  to  deal  abstractly  with  the 
ideas  which  a  common  signification  awakens  ;  they 
know  how  to  see  facts  beneath  the  conventional  pic- 
ture of  them  which  words  give. 

Nevertheless,  the  explanation  we  have  just  entered 
upon  is  not  useless  ;  it  will  justify  the  want  of  har- 
mony that  will  often  be  found,  without  doubt,  between 
the  names  given  to  phenomena  and  our  mode  of  ap- 
preciating them. 


SOUND   AND    LIGHT.  55 


CHAPTER  II. 

SOUND  AND   LIGHT. 

I. 

Nature  and  Mechanical  Equivalent  of  Sound. 

IT  has  been  known  for  a  long  time  that  sound  is 
the  effect  of  the  vibration  of  bodies,  propagated  either 
through  the  air  or  some  other  medium.  Acoustic 
phenomena  are,  so  to  speak,  visible  to  the  naked  eye  ; 
their  nature  was  likewise  known  at  an  early  period. 
If  a  plate  of  copper  be  firmly  secured  by  one  of  its 
sides,  and  a  bow  drawn  across,  the  free  edge,  the  eye 
perceives  the  vibration  of  the  plate.  Again,  if  the 
parchment  of  a  drum,  upon  which  fine  sand  has  been 
scattered,  be  exposed  to  agitated  air,  the  disturbance 
of  the  sand  betrays  that  of  the  air,  and  its  grains, 
driven  from  the  parts  that  are  most  shaken,  are  seen 
to  collect  along  the  lines  when  the  air  and  parchment 
are  in  a  state  of  rest.  The  rapidity  of  the  propaga- 
tion of  sound  is  itself  easily  appreciable  by  the  senses. 
Everybody  knows  that  if  a  cannon  be  fired  off  at  a 


$6         UNITY  OF  NATURAL  PHENOMENA. 

distance,  the  light  is  seen  much  sooner  than  the  report 
is  heard  ;  so  that  it  can  be  easily  ascertained  how 
many  seconds  sound  requires  to  pass  through  a  given 
interval  of  space.  Open  to  direct  experiment,  the 
principles  of  acoustics  have  long  been  viewed  in 
their  true  light,  and  it  has  not  been  necessary  to  im- 
agine, for  their  explanation  and  orderly  arrangement, 
either  a  special  fluid  or  a  particular  force.  Sound  is 
seen  to  be  a  vibratory  movement,  produced  by  a  cer- 
tain impulse,  and  propagated  through  a  medium. 
There  has  not  been  introduced  into  physics  either  a 
sonorous  fluid  or  a  sonorous  force. 

We  can  say,  then,  but  a  few  words  concerning 
sound.  Let  us  observe,  however,  that  the  study  of 
sonorous  vibrations,  considered  in  its  relations  to  the 
history  of  science,  possesses  a  peculiar  interest  for  us. 
These  are  the  first  vibratory  movements  which  were 
well  understood,  and  on  the  day  in  which  they  were 
exactly  defined  was  laid  one  of  the  firmest  foundations 
of  the  new  physics.  The  facts  revealed  by  this  study 
aided  in  a  powerful  manner  those  great  minds  which 
established  the  theory  of  light.  Between  sonorous 
and  luminous  vibrations  many  analogies  have  been 
sought  for  and  found.  Great  dissimilarities  have  also 
been  encountered.  Here  is  one  of  the  most  important, 
which  we  mention  here,  although  it  is  soon  v  to  be  re- 


SOUND   AND   LIGHT.  57 

ferred  to  again.  The  sonorous  vibration  takes  place  in 
the  direction  of  the  propagation  of  the  sound  ;  each 
molecule  of  the  air  that  has  been  set  in  motion 
executes  a  to-and-fro  movement  along  the  same  line 
in  which  the  sound  is  propagated.  On  the  other  hand, 
the  luminous  vibration  takes  place  in  a  direction  per- 
pendicular to  the  ray  of  light.  The  points  of  resem- 
blance and  dissimilarity  revealed  by  the  study  of  the 
motions  of  light  and  sound  afford  us  at  the  outset  a 
primary  view  of  the  problems  which  the  new  physics 
encounter,  and  of  the  methods  it  is  able  to  employ  for 
solving  them. 

We  have  still  another  instance  of  the  kind  of  inves- 
tigation demanded  by  this  new  science  when  we  pro- 
pound a  question  apropos  of  sound  that  will  succes- 
sively arise  in  regard  to  all  physical  phenomena.  We 
have  said  that  these  various  phenomena  are  susceptible 
of  being  transformed  into  each  other,  and  we  are  thus 
led  to  look  for  a  common  measure  in  the  dynamic 
effect  which  they  represent.  What  is  the  dynamic 
effect  of  a  sound  ?  or,  to  employ  a  term  introduced  into 
the  language  of  science  by  the  study  of  heat,  what  is 
the  mechanical  equivalent  of  sound  ?  Let  us  take  a 
bell,  and  strike  it  with  a  hammer  ;  we  shall  be  able  to 
calculate  exactly  the  mechanical  work  due  to  the 
stroke  of  the  hammer.  This  will  be  a  certain  num- 


58        UNITY  OF  NATURAL  PHENOMENA. 

ber  of  kilogrammetres.*  The  bell  will  vibrate,  and 
we  shall  be  able  to  measure  the  amplitude  of  its  vibra- 
tions by  means  of  a  luminous  ray  reflected  upon  a 
small  mirror  attached  to  the  bell ;  this  is  a  method 
often  employed  in  acoustics  to  amplify  the  oscillations, 
and  to  render  them  visible.  If  we  make  in  this  man- 
ner a  series  of  experiments,  and  if  we  compare  the 
figures  which  express*  the  shocks  with  those  which 
express  the  amplitude  of  the  oscillations,  we  shall  be 
able  to  condense  the  result  of  this  examination  into  a 
formula  which  will  give  us  an  idea  of  the  sonorous 
effect  of  different  blows. 

But  shall  we  in  this  manner  obtain  a  true  mechani- 
cal equivalent  of  sound  ?  Shall  we  be  able  to  say 
that  the  unit  of  sound  is  equivalent  to  so  many  kilo- 
grammetres ?  To  -do  this,  it  would  be  necessary  to 
begin  by  determining  the  value  of  a  unit  of  sound. 
We  distinguish  in  sound  several  properties  ;  it  has 

*  The  kilogrammetre  is  the  work  represented  by  a  kilogramme 
raised  to  the  height  of  a  meter.  The  English  equivalent  of  this 
term  is  "foot-pound."  The  quantity  of  heat  necessary  to  raise 
one  pound  of  water  one  degree  Fahrenheit  in  temperature,  is 
competent  to  raise  a  weight  of  seven  hundred  and  seventy-two 
pounds  a  foot  high.  By  the  French  method  of  reckoning,  the 
quantity  of  heat  necessary  to  raise  a  kilogramme  (2.2  pounds) 
of  water  one  degree  Centigrade  in  temperature,  is  sufficient 
to  raise  a  weight  of  four  hundred  and  twenty-five  kilogrammes 
to  the  height  of  a  meter  (39.37  inches).  —  Translator. 


SOUND    AND    LIGHT.  59 

pitch,  which  depends  upon  the  number  of  vibrations, 
intensity,  which  depends  upon  their  amplitude,  quality, 
which  depends  upon  more  complex  conditions.  What 
phenomenon  shall  be  selected  for  comparing  different 
sounds  with  each  other,  while  keeping  account  of  all 
their  effects  ?  Hitherto  such  a  question  does  not 
seem  to  have  demanded  consideration.  Interest  has 
been  felt  alone  in  the  number  of  the  vibrations  upon 
which  musical  theories  depend. 

To  tell  the  truth,  we  do  not  see  that  there  is  practi-  ' 
cally  any  special  utility  in  selecting  a  sound  unit  which 
shall  correspond  to  the  conditions  we  have  just  indi- 
cated. We  shall  not  insist,  then,  upon  this  point,  and 
we  have  only  mentioned  it  in  order  to  show  one  of  the 
new  aspects  presented  by  physical  studies. 

It  has  always  been  one  of  the  chief  difficulties  of 
the  exact  sciences  to  determine  suitably  the  units  by 
which  phenomena  must  be  compared.  This  selection 

j)f  units  possesses  now  an  especial  importance  from 

* 
the   new   standpoint  at  which  physicists  are  placed. 

We  are  thus  confronted  here  with  a  capital  question, 
which  demands  some  elucidation.  If  we  have  only 
touched  upon  it  with  regard  to  sound,  it  is  because  we 
await  an  opportunity  to  treat  it  with  more  profit,  for 
we  must  necessarily  encounter  it  at  nearly  every  step 
of  the  way. 


60        UNITY  OF  NATURAL  PHENOMENA. 


II. 


The  Nature  of  Light  and  of  Interference.  —  Universal- 
ity of  this  last  Phenomenon. 

ACOUSTICS  teaches  us  that  sound  is  a  vibratory 
motion,  be  it  of  air,  water,  or  of  any  other  material 
medium  analogous  to  these.  In  examining  optical 
phenomena,  we  shall  presently  behold  ether  appearing 
as  the  agent  of  the  luminous  wave,  and  this  conception 
of  ether  will  soon  become,  as  it  were,  the  bond  of  all 
the  ideas  which  pertain  to  the  unity  of  physical 
forces. 

Let  us  take  a  prism  composed  of  two  plates  of 
glass,  separated  by  sulphide  of  carbon,  and  place  it  in 
the  path  of  a  beam  of  solar  rays,  and  receive  the  im- 
age of  this  beam  upon  a  screen.  This  image,  as  is 
known,  is  called  a  spectrum  ;  the  screen  will  show  us 
luminous  rays  of  different  colors,  unequally  refracted, 
by  their  passage  through  the  prismatic  mass  of  the 
sulphide  of  carbon.  The  red  rays  are  least  deflected, 
and  are  consequently  found  towards  the  edge  of  the 
prism  ;  then,  proceeding  from  the  edge  to  the  base, 
come  orange,  yellow,  green,  blue,  indigo,  violet. 

If,  now,  we  examine  the  spectrum  with  attention, 
the  phenomenon  will  not  be  simply  a  luminous  one. 


SOUND    AND    LIGHT.  6l 

It  will  acquaint  us  with  the  calorific  and  chemical 
properties  of  the  solar  beam.  Let  us  receive  the 
spectrum  upon  a  plate  pierced  with  a  narrow  slit, 
through  which  the  rays  can  act  upon  a  thermo-electric 
pile,  and  let  us  move  the  slit  through  the  whole  ex- 
tent of  the  spectrum,  beginning  with  the  violet  por- 
tion. So  long  as  we  remain  in  the  violet,  the  -indigo, 
the  blue,  and  even  the  green,  the  needle  of  the  thermo- 
scopic  apparatus  will  be  deflected  but  slightly.  It  will 
indicate  a  heat,  increasing  according  as  the  slit  crosses 
the  yellow,  next  the  orange,  then  the  red ;  but  let  us 
pass  beyond  the  red,  and  enter  the  dark  part  of  the 
spectrum  ;  we  shall  here  find  the  maximum  of  heat* 

Thus  there  is,  beyond  the  visible  image  of  the  solar 
beam,  a  warm  spectrum  which  we  cannot  see.  If  the 
rays,  which  are  refracted  on  one  side  of  the  spectrum 
beyond  the  red,  have  an  especial  aptitude  for  produ- 
cing heat,  those  which  are  refracted  upon  the  other  side, 
beyond  the  violet,  have  an  especial  aptitude  for  excit- 
ing chemical  action.  These  chemical  rays  may  be 
rendered  visible  by  a  contrivance  well  known  in  the 


*  From  an  examination  of  the  distribution  of  heat  in  the  spec- 
trum of  the  electric  light,  it  appears  that  the  maximum  of  inten- 
sity is  in  the  dark  region,  beyond  the  red;  and  further,  that  if  all 
the  visible  rays  were  conveyed  to  a  focus,  its  heat  would  be  only 
one  ninth  of  that  produced  at  the  dark  focus  of  the  invisible  rays. 
—  Translator* 


62        UNITY  OF  NATURAL  PHENOMENA. 

laboratory.  Take  a  sheet  of  paper,  the  lower  part  of 
which  is  moistened  with  a  solution  of  sulphate  of 
quinine,  while  the  upper  part  remains  dry.  Let  the 
image  of  the  solar  ray  fall  upon  this  sheet,  the  spec- 
trum preserves  at  the  top  of  the  sheet  its  ordinary  ap- 
pearance, while  in  the  moistened  portion  a  brilliant 
phosphorescence  appears  beyond  the  violet  rays. 

Thus  the  spectrum  extends  beyond  its  visible  por- 
tion in  two  directions,  to  the  right  and  to  the  left,  and 
analysis  can  distinguish  in  it,  beyond  the  luminous  rays, 
calorific  and  chemical  rays,  the  latter  more  particularly 
deviated  towards  the  violet  portion,  the  former  more 
especially  refracted  towards  the  red  portion. 

All  forms  of  light  thus  far  known  exhibit  three 
kinds  of  rays.  Their  phenomena  vary,  it  is  well 
known,  in  a  certain  degree  with  the  means  of  obser- 
vation. And  in  the  first  place,  simply  to  use  a  prism, 
produces  a  spectrum  in  a  manner  merely  conven- 
tional ;  the  prism  disperses  differently  the  rays  of 
different  refrangibility ;  it  leaves  the  red  rays  more 
crowded  together  ;  on  the  contrary,  it  gives  more 
breadth  to  the  violet  portion.  We  may,  by  other 
means,  obtain  a  spectrum  in  which  the  different  rays 
better  preserve  their  relative  value.  The  nature  of 
the  prism  also  changes  the  relation  between  the  lumi- 
nous, calorific,  and  chemical  rays.  If  a  solar  ray  be 


SOUND   AND    LIGHT.  63 

received  upon  a  prism  of  water,  the  maximum  of  heat 
will  appear  in  the  yellow,  upon  'a  prism,  of  common 
glass  in  the  red,  upon  a  prism  of  flint  glass  beyond 
the  red,  upon  one  of  rock  salt  far  beyond  the  red  in  the 
entirely  dark  portion.  It  would  likewise  be  necessary 
to  take  into  account  the  nature  of  the  luminous  source. 
But  passing  over  these  details,  we  were  desirous  only 
of  showing  how,  in  every  emission  of  light,  there  is 
found,  in  addition  to  luminous  action,  properly  so 
called,  calorific  and  chemical  action.  We  succeed  in 
dividing  these  three  actions,  but  not  without  difficulty, 
to  such  a  degree  do  they  appear  to  be  commingled. 
Let  us  not,  then,  forget  this  ready-made  synthesis, 
which  is  offered  to  us  at  the  outset.  If,  after  having 
studied  separately  heat,  light,  and  affinity,  we  arrive  at 
the  law  which  unites  these  phenomena,  let  us  remem- 
ber that  we  found  them  united,  and  that  we  have  sepa- 
rated them  in  order  the  better  to  examine  them.  For 
the  present  we  must  continue  our  analysis,  leaving 
aside  heat  as  well  as  chemical  action,  and  occupying 
ourselves  only  with  light. 

What  is  light  ?  This  subject  has  given  full  play  to 
the  imagination  of  the  earlier  physicists.  Some  lo- 
cated in  the  eye  a  visual  force  ;  this  force  projected 
rays  which  came  in  contact  with  objects.  Others 
supposed,  on  the  other  hand,  that  objects  emitted  all 


64        UNITY  OF  NATURAL  PHENOMENA. 

around  them  an  infinite  number  of  little  images,  which 
entered  the'  eyes  of  men  and  of  animals.  It  was 
hardly  possible  to  discuss  seriously  the  nature  of  light 
before  the  structure  of  the  eye  was  known,  and  the 
image  of  objects  had  been  seen  formed  upon  the  retina, 
as  upon  the  end  of  a  camera  obscurd.  The  retina  thus 
impressed  transmits  the  sensation  to  the  optic  nerve. 
But  how  is  the  retina  thus  impressed  ?  how  is  the 
image  formed  there  ? 

Newton  supposed  that  luminous  bodies  shoot  out 
little  corpuscles,  the  shock  of  which  excites  the  retina. 
This  is  the  famous  theory  of  emission,  which  gave  rise, 
towards  the  close  of  the  seventeenth  century,  to  such 
hot  disputes.  Newton  had  established,  while  making 
use  of  his  hypothesis,  the  principal  laws  of  optics, 
those  of  reflection  and  those  of  refraction.  Neverthe- 
less difficulties  continued  to  exist.  Other  optical  phe- 
nomena, more  complicated, — polarization  and  double 
refraction,  —  could  not  be  explained  by  the  Newtonian 
theory.  Questions  were  put  to  Newton,  to  which  his 
hypothesis  gave  no  answer  :  "  Where  does  the  light 
go  when  it  is  extinguished  ?  Whither  go  the  cor- 
puscles which  are  constantly  leaving  the  sources  of 
light  ? " 

Descartes  advanced  the  idea  that  a  subtile  matter 
fills  the  planetary  spaces.  This  conjecture,  by  which 


SOUND  AND   LIGHT.  65 

he  had  vainly  attempted  to  explain  astronomical  phe-vv 
nomena,  was  eagerly  seized  upon,  and  applied  to  light. 
Malebranche  was  among  the  first  to  suspect  that  light 
is  produced  by  the  undulations  of  an  ether,  and  that 
the  differences  in  the  length  of  the  waves  are  the 
causes  of  the  different  colors.  Huyghens  adopted  this 
system,  and  subjected  the  deductions  to  mathematical 
calculation.  Thus  admitted  into  science  under  a  hy- 
pothetical title,  the  existence  of  the  ether  became  more 
and  more  probable  in  proportion  as  experiment  justi- 
fied the  conclusions  drawn  from  this  principle. 

Nevertheless,  Newton  supported  with-  energy  the 
theory  of  emission,  and  accumulated  in  its  defence 
proofs,  a  great  many  of  which  would  appear  very 
whimsical  to-day.  Euler  supported  Huyghens,  and 
beheld,  in  a  kind  of  classification  of  the  phenomena 
which  affect  our  senses,  an  argument  in  favor  of  undu- 
lation. "  In  order  to  perceive  an  object  by  touch," 
said  he,  "  it  is  necessary  that  we  be  in  contact  with 
the  object  itself.  With  regard  to  odors,  we  know  that 
they  are  produced,  by  material  particles  which  issue 
from  the  volatile  body.  As  regards  hearing,  there  is 
nothing  detached  from  the  sounding  body.  The  dis- 
tance at  which  our  senses  recognize  the  presence  of 
objects  is  nothing  in  the  case  of  touch,  small  in  the 
case  of  smelling,  somewhat  great  in  the  case  of  hear- 
5 


66         UNITY  OF  NATURAL  PHENOMENA. 

ing,  while  in  the  case  of  sight  this  distance  becomes 
considerable.  Pursuing  this  progression,  we  must 
believe  that  the  sense  of  sight  perceives  in  the  same 
manner  as  that  of  hearing,  and  not  in  the  same 
manner  as  the  sense  of  smell ;  it  must  be  supposed 
that  luminous  bodies  vibrate  like  sonorous  bodies,  in- 
stead of  emitting  particles  like  volatile  substances." 

During  the  debate  there  were  brought  forward  some 
curious  facts,  observed  near  the  middle  of  the  seven- 
teenth century,  by  Father  Grimaldi,  a  Bolognese  monk, 
who  left  behind  him  a  very  original  treatise  upon  op- 
tics (De  Lumine,  Coloribus,  et  Iride :  Bologne,  1665).  If 
a  shutter  be  pierced  with  a  very  small  hole,  and  the 
luminous  cone  which  passes  through  the  orifice  be 
examined,  it  is  observed  that  the  cone  is  much  less 
acute  than  would  be  expected,  considering  only  the 
rectilinear  transmission  of  the  rays.  The  experiment 
becomes  still  more  striking  if  there  be  interposed  in 
the  path  of  the  luminous  ray  a  second  shutter  pierced 
with  a  new  hole,  when  it  is  readily  apparent  that  the 
rays  of  the  second  cone  are  more  divergent  than  those 
of  the  first.  If  a  fine  thread  is  introduced  into  the 
luminous  cone,  and  its  shadow  projected  upon  a 
screen,  the  shadow  appears  surrounded  by  three  col- 
ored fringes,  and  there  are  also  seen  in  this  shadow  one 
or  more  luminous  rays.  Let  the  image  of  the  orifice 


SOUND    AND   LIGHT.  6/ 

in  the  shutter  be  received  upon  a  screen,  and  a  white 

** 

circle  is  seen  surrounded  by  a  dark  ring,  next  a  white 
ring,  more  brilliant  than  the  central  portion,  then  a 
second  dark  ring,  and  finally  another  very  faint  white 
ring.  If  in  the  shutter  with  which  the  experiment  is 
made,  two  very  small  holes  are  pierced  at  a  distance 
from  each  of  one  or  two  millimetres,  and  the  two 
images  received  upon  a  screen  in  such  a  manner  that 
they  overlap  each  other,  it  is  found  that  -in  the  len- 
ticular segment  formed  by  the  overlapping  of  the  im- 
ages, the  circles  are  more  obscure  than  in  the  part 
where  they  are  separated.  Thus  it  appears  that  by 
adding  light  to  light  darkness  is  produced. 

These  curious  facts,  minutely  described  by  Father 
Grimaldi,  appear  to  us  quite  decisive,  now  that  we 
grasp  their  real  meaning.  It  seems  to  us  that  they 
should  have  caused  the  system  of  undulations  to  have 
triumphed  forthwith ;  but  even  those  who  could  ap- 
preciate their  value  in  the  seventeenth  century,  were 
far  from  drawing  from  them  all  their  consequences. 
These  experiments  at  least  served  to  feed  the  dispute.  * 
Corpuscles,  said  Huyghens,  coming  directly  from  the 
sun,  and  passing  through  a  small  aperture,  would  form, 
in  escaping  from  the  holes,  a  straight  cylinder,  and 
not  a  cone.  The  conical  form  is  proof  of  a  motion 
which  is  propagated  in  a  line  lateral  to  the  luminous 


68        UNITY  OF  NATURAL  PHENOMENA. 

ray.  Newton  retorted,  "  if  light  is  a  motion,  it  would 
not  remain  confined  in  a  narrow  cone ;  it  should  spread 
itself  in  every  direction,  and  scatter  itself  in  a  circu- 
lar manner  around  each  point  of  disturbance." 

"Without  doubt,"  replied  Huyghens,  "at  every  point 
of  the  luminous  ray  spherical  undulations  go  out  in 
the  direction  lateral  to  this  ray,  and  extend  into  all  the 
surrounding  space  ;  but  they  are  not  often  enough 
repeated  to  produce  the  sensation  of  light.  They  do 
not  yield  to  a  force  as  strong  as  do  those  which  occur 
in  the  same  direction  as  the  ray,  and  they  destroy 
each  other  in  their  confusion."  * 

The  first  scientist  who  saw  all  that  could  be  in- 
ferred from  these  experiments  of  Grimaldi  was  Thom- 
as' Young,  that  sagacious  traveller,  who  developed  sev- 
eral branches  of  physical  science,  and  who  discovered 
the  key  to  the  Egyptian  hieroglyphics.  The  re- 
searches of  Young  were  continued  by  Arago  and 
Fresnel,  and  more  recently  by  M.  M.  Fizeau  and 
Foucault.  The  labors  of  all  of  these  have  given  a  com- 
plete explanation  of  the  fringes  of  light  pointed  out 

*  In  accounting  for  the  fact  that  light  is  not  diffused  beyond 
the  rectilinear  space  when  it  passes  through  an  aperture,  Huy- 
ghens says,  "  Although  the  partial  waves  produced  by  the  parti- 
cles comprised  in  the  aperture  do  diffuse  themselves  beyond  the 
rectilinear  space,  these  waves  do  not  concur  anywhere  except  in 
front  of  the  aperture."  —  Translator. 


SOUND   AND    LIGHT.  69 

by  Grimaldi,  and  the  theory  of  interferences  which 
they  have  founded  is  one  of  the  most  glorious  achieve- 
ments of  modern  thought. 

The  principle  of  interferences  is  difficult  to  grasp. 
A  ray  of  light,  according  to  what  we  have  just  said,  is 
the  propagation  of  a  motion  in  which  the  atoms  of 
the  ether  oscillate  around  their  point  of  equilibrium. 
They  are  then  endowed  with  a  certain  velocity  in  one 
direction  during  the  first  half  of  this  undulation,  and 
with  the  same  velocity  in  the  opposite  direction  dur- 
ing the  second  half.  Let  us  suppose,  now,  that  we 
can  arrange  two  rays  issuing  from  the  same  surface, 
and  that  by  any  contrivance  whatever  one  of  the  two 
has  been  retarded  behind  the  other  a  half  undulation, 
if  two  rays  be  placed  upon  each  other  at  the  point 
of  superposition,  the  atoms  of  either  will  remain  im- 
movable, since  they  will  be  equally  solicited  to  motion 
in  both  directions ;  there  will  then  be  at  this  point 
an  absence  of  luminous  motion,  or  darkness.  There 
will  be  an  increase  of  light  when  the  amount  of  retar- 
dation is  two  demi-undulations,  darkness  when  it  is 
three,  and  so  on. 

By  means  of  experiments  based  upon  this  principle, 
it  has  been  possible  to  measure  the  length  and  the 
duration  of  the  waves  which  correspond  to  the  differ- 
ent colors  of  the  spectrum.  The  wave  increases  in 


7O        UNITY  OF  NATURAL  PHENOMENA. 

length  and  in  duration  from  the  red  to  the  violet ;  its 
length,  expressed  in  millimetres,  is  0.000738,  at  the 
extreme  red  ;  0.0005  5  3,  at  the  middle  of  the  yellow ; 
0.000369  at  the  extreme  violet.* 

It  has  been  proved,  moreover,  by  particular  methods, 
that  the  same  law  of  decrease  extends  to  the  invisible 
portions  of  the  spectrum  ;  the  calorific  vibrations  be- 
yond the  red  are  slower  and  longer.  The  longest 
wave  of  obscure  heat  which  it  has  been  possible  to 
measure  up  to  this  time  is  0.001830  millimetres.  As 
regards  the  duration  of  the  waves,  a  general  idea  may 

be  obtained  from  knowing  that  the  vibration  of  the 

* 

yellow  ray  lasts  530  trillionths  of  a  second.  It  is, 
moreover,  a  recognized  fact  that  the  eye  cannot  per- 
ceive a  sensation  of  light  unless  it  continue  at  least 
several  hundredths  of  a  second ;  there  must  be  then 
several  billions  of  waves  to  produce  the  sensation  of 
light. 

We  here  see  confirmed  by  experiment  the  reason- 
ing which  we  just  now  put  in  the  mouth  of  Huyghens, 

*  According  to  Tjndall,  the  length  of  a  wave  of  mean  red 
light  is  about  the  39,oooth  of  an  inch ;  that  of  mean  violet  light, 
the  57, 5ooth  of  an  inch.  Taking  the  velocity  of  light  at  185,000 
miles  per  second,  as  determined  by  Foucault,  we  have  the  num- 
ber of  waves  of  red  light  which  enter  the  eye  each  second  as 
458,142,400,000,000.  The  number  of  waves  which  enter  the  eye  to 
cause  the  sensation  of  violet  color  is  about  one  third  more  than 
this,  being  upwards  of  700  trillions.  —  Translator. 


SOUND   AND   LIGHT.  7 1 

and  the  limits  within  which  the  waves  once  departed 
from  the  line  of  luminous  shock,  are  no  longer  fre- 
quent enough  to  produce  light. 

It  may  be  understood,  without  dwelling  further  upon 
this  point,  how  important  the  study  of  interferences 
becomes  in  the  new  physics.  The  interest  pertaining 
to  it  does  not  remain  restricted  within  the  limits  of 
optics,  it  extends  to  every  branch  of  science.  When- 
ever a  vibratory  motion  exists  we  may  expect  to  find 
the  phenomena  of  interferences. 

Acoustics,  for  example,  has  its  own,  which  easily 
admit  of  proof.  Let  us  take  a  plate  of  copper,  sup- 
ported horizontally  upon  an  upright  stand,  and  having 
scattered  fine  sand  over  it,  let  us  draw  a  bow  rapidly 
over  one  of  its  edges.  The  surface  is  divided  into 
eight  triangles  ;  the  adjacent  triangles  vibrate  in  an 
opposite  direction,  while  those  which  do  not  touch 
each  other  vibrate  in  a  similar  direction.  The  fine 
sand  gives  evidence  of  this  state  of  things  by  arran- 
ging itself  along  the  lines  which  cross  the  surface. 
There  is  here  a  state  of  repose,  because  there  is  an 
equal  tendency  to  two  opposing  motions.  These  con- 
trary impulses,  which  go  out  from  the  different  parts 
of  the  metal  plate  in  order  to  cross  each  other  in  the 
surrounding  air,  must  produce  therein  true  phenomena 
of  interferences,  for  sometimes  they  mutually  strength- 


72        UNITY  OF  NATURAL  PHENOMENA. 

en  each  other,  and  sometimes  they  oppose  each  other. 
This  is  demonstrated  by  a  very  simple  instrument  —  a 
tube,  one  end  of  which  forms  a  funnel  over  which  a 
membrane  is  stretched,  while  the  other  extremity  ter- 
minates in  two  branches,  forming  an  angle  with  each 
other.  Having  now  the  ear  placed  against  the  funnel, 
the  two  terminal  branches  of  the  tube  are  passed  over 
the  surface  of  the  plate  of  copper,  when  it  is  easily 
observed  that  the  sound  is  very  weak  when  they  are 
near  the  centre  of  two  contiguous  triangles,  and  that 
it  grows  louder,  on  the  contrary,  when  they  touch  two 
triangles  vibrating  in  the  same  direction. 

We  are  now  acquainted  with  sonorous  interferences 
and  luminous  interferences,  but  above  all  we  must 
expect  to  see  these  phenomena  of  universal  occurrence 
in  physics.  They  will  appear  necessarily  under  the 
most  varied  forms,  according  to  the  mode  of  motion 
which  produces  them,  and  according  to  the  nature  of 
the  organ  whose  office  it  is  to  perceive  them.  In 
every  case,  the  researches  which  will  be  made  in  this 
direction  will  be  powerfully  aided  by  the  magnificent 
works  that  have  marked  the  study  of  luminous  inter- 
ferences. 


SOUND   AND   LIGHT.  73 


III. 


Conclusions  as  to  the  Ether  drawn  from  Luminous 
Phenomena. 

WE  must  now  consider  more  closely  this  idea  of  the 
Ether,  to  which  we  have  been  led  by  the  phenomena 
of  light ;  we  must  clearly  define  it,  and  remove  it  from 
the  controversies  to  which  it  has  given  rise. 

What  is  the  ether  ?  Is  it  really  imponderable  ?  and 
in  that  case  what  does  this  property  mean  ?  In  what 
does  it  differ  from  ordinary  matter  ?  in  what  does  it 
resemble  it  ?  What  are  its  relations  with  it  ?  Is  it 
not  a  little  strange  to  introduce  here,  at  the  very  time 
when  we  are  banishing  from  science  a  host  of  con- 
ventional entities  and  abstract  forces,  the  idea  of  a 
medium,  which  is,  so  to  speak,  immaterial  ? 

We  shall  have  replied  to  this  last  question  when  we 
shall  have  shown  that  the  ether,  according  to  our  con- 
ception of  it,  does  not  possess  the  fantastic  properties 
that  are  sometimes  ascribed  to  it. 

We  conceive  of  a  simple  gas,  oxygen  for  example, 
as  an  assemblage  of  elementary  molecules,  animated 
with  motion,  which  strike  against  each  other,  from 
which  result  the  expansive  force  of  the  gas,  and  the 
pressure  that  it  exercises  upon  the  bodies  in  which  it 


74        UNITY  OF  NATURAL  PHENOMENA. 

is  contained.  This  idea  will  become  clearer  when  we 
seek  to  inform  ourselves  concerning  the  interior  con- 
stitution of  bodies,  profiting  by  the  ideas  generally 
adopted  regarding  the  nature  of  heat ;  but  for  the 
present  we  can  accept  it  as  a  kind  of  primitive  con- 
ception, with  which  the  mind  may  be  satisfied  while 
waiting  for  the  testimony  of  science.  It  is  under  this 
simple  form  that  we  conceive  of  ether,  and  we  add, 
that  its  elements  are  atoms ;  that  is  to  say,  that  they 
cannot  be  divided.  If  the  objection  be  offered  that  it 
is  difficult  to  comprehend  that  they  are  really  indi- 
visible, we  reply,  that  it  is  sufficient  for  us  to  con- 
ceive that  they  comport  themselves  as  such,  for  no 
one  has  the  pretension  to  penetrate  either  the  in- 
finitely small  or  the  infinitely  great.  The  atoms 
of  the  ether  are  endowed  with  motion,  which  they 
communicate  to  each  other,  and  to  surrounding 
bodies. 

Are  these,  then,  immaterial  ?  Certainly  not.  Two 
properties  belong  to  matter  —  impenetrability  and  in- 
ertia. The  -ethereal  atoms  are  impenetrable  at  the 
outset ;  they  are  so  by  definition.  They  are  also  in- 
ert ;  they  have  received  the  motion  with  which  they 
are  endowed,  and  they  lose  it  only  in  communicating  it. 
Nothing  distinguishes  ether,  then,  from  matter ;  and 
when  we  just  now  presented  it,  in  the  preceding  lines, 


SOUND   AND   LIGHT.  75 

as  awakening  the  idea  of  a  medium,  so  to  speak,  im- 

*i 
material,  we  made,  be  it  understood,  a  pure  concession 

to  certain  usages  of  language.     Our  ether  is  material, 
just  as  oxygen  is. 

But  it  is  imponderable  !  Yes,  and  we  here  confront 
a  very  delicate  explanation.  We  should  make  our- 
selves better  understood  if  we  should  here  show,  in 
some  detail,  under  what  aspect  universal  attraction  ap- 
pears in  the  new  order  of  ideas  upon  which  we  are 
entered  ;  but  this  is  a  point  of  view  which  we  shall 
unfold  only  in  the  course  of  this  work.  Under  what- 
ever form  the  interior  state  of  an  ordinary  molecule 
may  be  conceived,  whether  it  be  regarded  as  a  primi- 
tive substance,  or  be  viewed  as  a  reunion  of  ethereal 
atoms  associated  together  according  to  certain  laws,  it 
must  be  admitted  that  this  molecule  possesses  a  mass 
much  larger  than  each  of  the  atoms  of  the  ether. 
This  granted,  if  two  molecules  are  in  the  presence  of 
each  other,  the  surrounding  ether  impinging  upon 
them  both  in  every  direction,  there  will  result  from 
this  very  situation  a  disposition  to  approach,  which  is 
known  by  the  name  of  attraction  or  gravity.  Let  us 
remain  satisfied  for  the  present  with  this  summary  ex- 
planation, which  will  be  completed  in  the  sequel.  It 
is  sufficient  now  to  make  it  evident  how  ether  is  im- 
ponderable ;  if  two  molecules  tend  to  approach  each 


76  UNITY   OF   NATURAL   PHENOMENA. 

other,  it  is  because  their  presence  interrupts  the  uni- 
formity of  the  ethereal  impulsions  in  just  such  a  man- 
ner that  they  are  necessarily  forced  one  against  the 
other.  Nothing  of  a  similar  character  will  be  discov- 
ered when  we  examine  ether  itself  in  its  own  motion  ; 
it  moves  in  all  directions,  and  there  would  appear  to  be 
'nothing  to  force  it  in  one  direction  rather  than  in  an- 
other. Thus  this  fluid  produces  attraction  in  matter 
without  itself  being  subjected  to  it ;  it  confers  gravity 
upon  bodies,  and  itself  is  imponderable. 

If,  then,  we  wish  to  distinguish  ether  from  pondera- 
ble matter,  it  will  be  necessary,  in  order  to  employ  an 
accurate  term,  to  call  it  imponderable  matter.  Granted 
that  the  current  phrase  be  ether  on  the  one  hand  and 
matter  on  the  other,  we  shall  still  continue  to  use  the 
term,  as  we  have  done  already,  for  the  sake  of  brevity  ; 
we  shall  have  at  least  shown  what  is  expressed  by 
these  words,  and  we  shall  have  proved  that  the  impon- 
derability of  ether  must  be  admitted,  without  meaning 
thereby  to  confer  upon  this  fluid  a  title  of  immaterial- 
ity. Let  us  add  that  there  would  be  a  real  advantage 
in  getting  rid  of  the  term  ether,  which  incurs  the  risk 
of  always  possessing  more  or  less  of  mysticism. 

We  have  represented  the  ether  as  an  assemblage  of 
atoms  which  strike  each  other,  and  rebound  in  all  di- 
rections. Here  a  capital  objection  presents  itself,  and 


SOUND   AND   LIGHT.  77 

we  must  attack  it.     How  do  these  atoms  rebound  ? 

V 

Are  they  elastic  ?  The  notion  of  an  atom  and  of 
elasticity  are  incompatible.  We  can  understand  the 
elasticity  of  a  compound  molecule  ;  the  different  parts 
of  the  molecule,  pressed  upon  by  an  external  force, 
are  displaced  while  being  compressed,  then  regain 
their  position  while  returning  the  impulsion  which 
they  have  received.  This  mechamism  supposes  a  void 
in  the  interior  of  the  molecule  ;  but  the  atom  is  im- 
penetrable, indivisible ;  it  does  not  enclose  a  void. 
There  is  here  a  serious  difficulty.  Huyghens,  it  is 
necessary  to  state,  ascribed  to  the  atoms  of  the  ether 
an  elastic  force.  What  did  he  understand  by  this  ? 
Did  he  then  regard  them  as  compound  corpuscles  ? 
The  difficulty  had  only  changed  place.  Fortunately 
mechanics  have  succeeded  in  solving  this  problem, 
and  the  beautiful  researches  of  Poinsot  upon  revolving 
bodies  explain  how  the  ethereal  atoms  may  rebound 
from  each  other  without  being  elastic.*  It  is  suffi- 
cient for  understanding  this  effect  to  suppose  that 

*  "  It  is  just  as  easy  to  conceive  of  a  vibrating  atom  as  to  con- 
ceive of  a  vibrating  cannon-ball;  and  there  is  no  more  difficulty 
in  conceiving  of  this  Ether,  as  it  is  called,  which  fills  space,  than 
in  imagining  all  space  to  be  filled  with  jelly.  You  must  imagine 
the  atoms  vibrating,  and  their  vibrations  you  must  figure  as 
communicated  to  the  ether  in  which  they  swing,  being  propa- 
gated through  it  in  waves ;  these  waves  enter  the  pupil,  cross 


78        UNITY  OF  NATURAL  PHENOMENA. 

they  possess,  in  addition  to  their  motion  of  translation, 
a  rotatory  motion. 

From  the  theorem  formulated  by  Poinsot,  it  results 
that  a  hard  and  inelastic  body  may,  if  it  revolves,  be 
turned  aside  by  any  obstacle,  precisely  like  a  body  pos- 
sessed of  elasticity  ;  more  than  this,  there  is  often, 
after  the  blow,  a  greater  velocity  than  before,  because 
a  part  of  the  rotation  is  converted  into  a  motion  of 
translation.  In  general,  when  a  revolving  body  strikes 
against  an  obstacle,  it  cannot  lose  its  two  motions  at 
once  ;  at  farthest,  it  may  do  so  only  in  certain  theo- 
retical instances,  which  need  not  be  considered  here. 
If  the  shock  pass  through  the  centre  of  gravity  of  the 
body,  it  will  assist  its  onward  progress,  but  not  its 
rotation  ;  if  it  be  eccentric,  it  will  stop  the  rotation, 
but  not  the  forward  movement.  The  two  motions  will 
likewise  be  partly  transformed,  one  into  the  other,  in 
such  a  manner  as  to  produce  more  varied  phenomena. 

The  game  of  billiards  has  made  some  of  these  ef- 
fects familiar.  It  is  here  seen  how  the  rotation  of  a 
ball  operates  to  modify  both  its  direction  and  velocity 
when  a  blow  is  received.  In  the  illustration  cited, 
elasticity  combines  with  rotatory  motion  ;  but  it  is 

the  ball  of  the  eye,  and  break  upon  the  retina  at  the  back  of  the 
eye.  The  act  is  as  real  and  as  truly  mechanical  as  the  breaking  of 
the  sea-waves  upon  the  shore."  —  Heat  as  a  Mode  of  Motion,  p.  268. 


SOUND    AND    LIGHT.  79 

necessary  to  abstract  the  latter  phenomenon,  and^  to 
give  it  separate  consideration,  in  order  to  conceive 
how  the  ethereal  atoms  may  rebound  without  being 
elastic. 

Let  us  enter  a  little  farther  into  the  idea  of  these 
motions  ;  we  shall  see  the  hypothesis  of  the  rotation 
of  ethereal  atoms  explain,  in  a  certain  degree  at  least, 
a  phenomenon  of  capital  importance,  and  one  we  have 
already  mentioned. 

The  undulation  of  light,  we  have  said,  is  propagated 
in  a  direction  at  right  angles  to  the  luminous  ray,  and 
we  have  observed  that  in  this  respect  it  differs  from 
the  sonorous  undulation  which  takes  place  in  the 
same  direction  as  the  propagation  of  the  sound. 
There  is  nothing  to  astonish  us  in  the  manner  in 
which  the  luminous  wave  is  propagated,  and  we  find 
many  examples  of  it  in  nature.  If  a  stone  be  thrown 
into  the  water,  we  see  the  water  rise  in  waves  which 
are  perpendicular  to  the  direction  of  its  fall.  In  this 
case  it  is  evident  that  the  liquid  disturbed  by  the  stone 
moves  in  the  direction  in  which  it  meets  with  the  least 
resistance.*  A  similar  reason  was  assigned  by  Fresnel 


*  "In  the  case  of  sound,  the  vibrations  of  the  air-particles 
are  executed  in  the  direction  in  which  the  sound  travels.  They 
are  therefore  called  longitudinal  vibrations.  In  the  case  of  light, 
on  the  contrary,  the  vibrations  are  transversal,  that  is  to  say, 


8O        UNITY  OF  NATURAL  PHENOMENA. 

for  the  luminous  motion.  "  I  think,"  said  he,  "  that 
the  shock  is  communicated  to  the  ether  longitudinally, 
that  is  to  say,  in  the  direction  of  the  ray,  but  the  ether 
possesses  such  a  nature  that  it  can  only  respond  to  the 
impulse  by  a  lateral  vibration."  This  vague  explana- 
tion becomes  strikingly  definite  if  we  suppose  the 
ethereal  atoms  to  turn  upon  themselves. 

We  know  from  mechanics,  that  if  a  revolving  body 
receive  a  shock  perpendicularly  to  the  axis  of  rotation, 
the  centre  of  gravity  of  the  body  is  carried  at  right 
angles  to  the  direction  of  the  shock.  Strike  a  whirl- 
ing top,  it  will  jump  to  one  side.  There  is  a  well- 
?  known  experiment  upon  this  subject.  A  top  is  placed 
on  a  horizontal  plane,  and  while  it  sleeps,  if  the  plane 
be  inclined  from  south  to  north,  immediately  the  top 
moves  from  east  to  west ;  if  the  plane  be  inclined 
from  east  to  west,  it  moves  from  south  to  north. 
Thus  the  component  gravity  causes  the  top  to  move 
in  a  direction  at  right  angles  to  that  component.  The 
phenomenon  does  not  take  place,  of  course,  unless  the 
top  is  whirling,  and  there  is  no  such  result  while  it  is 
in  a  state  of  repose. 

the  individual  particles  of  ether  move  to  and  fro  across,  the  di- 
rection in  which  the  light  is  propagated.  In  this  respect  waves 
of  light  resemble  ordinary  water-waves  more  than  waves  of 
sound."  —  Tyndall,  Fragments  of  Science,  p.  284. 


SOUND   AND   LIGHT.  8 1 

Placed  at  this  point  of  view,  we  understand  without 
difficulty  how  the  rotation  of  the  ethereal  atoms  ac- 
counts for  their  lateral  displacement  during  the  lumi- 
nous impulse ;  their  transverse  vibration  will  appear 
not  only  possible,  but  even  necessary. 

This  explanation  we  borrow  from  the  books  of 
Father  Secchi  upon  the  Unity  of  the  Physical  Forces. 
The  inference  which  the  learned  abb6  has  drawn  from 
the  rotation  of  the  ethereal  atoms,  is  not  the  least  in- 
teresting feature  of  his  work.  While  we  are  dwelling 
with  some  detail  upon  the  transverse  motion  of  light, 
we  cannot  resist  the  desire  of  presenting,  in  opposi- 
tion to  the  hints  thrown  out  by  Father  Secchi,  the 
views  which  M.  de  Boucheporn  offers  upon  the  same 
subject  in  his  Principe  general  de  la  Philosophie  natii- 
relle.  This  digression  will  interrupt  the  orderly  pres- 
entation of  our  ideas ;  but  we  shall  at  least  acquaint 
our  readers,  by  a  brilliant  example,  with  those  bold 
conjectures  characteristic  of  M.  de  Boucheporn,  which 
he  knew  how,  with  infinite  art,  to  verify  in  fact.  See- 
ing his  point  of  departure  and  the  good  to  which  he 
arrives,  one  is  persuaded,  but  not  convinced. 

M.  de  Boucheporn  attributes  the  transverse  undula- 
tion to  the  friction  of  the  ether  against  the  revolving 
surface  of  the  sun.  This  hypothesis  furnishes  him  at 
once  with  the  explanation  of  the  phenomena  of  colors, 
6 


82        UNITY  OF  NATURAL  PHENOMENA. 

and  he  finds  its  confirmation  in  the  examination  of  the 
length  of  the  waves  which  characterize  the  principal 
tints  of  the  spectrum.  Let  us  follow  him  in  his  argu- 
ment. 

If  it  is  the  sun's  rotation  which  impels  the  ethereal 
atoms  in  a  direction  tangent  to  its  motion,  this  effect 
should  be  produced  in  a  very  different  manner  at  the 
different  points  of  the  solar  meridian  ;  it  would  neces- 
sarily decrease  in  energy  from  the  equator  to  the  poles. 
At  the  equator  the  friction  is  in  full  force,  while  at  the 
poles  it  is  nothing.  Between  the  equator  and  the  pole 
its  energy  decreases  according  to  the  radii  of  the  paral- 
lels, or  as  the  cosines  of  the  latitudes.  M.  de  Boucheporn, 
thereupon,  supposes  the  differences  in  the  lengths  of 
the  waves,  that  is  to  say,  the  differences  in  the  colors, 
correspond  to  the  impulses  given  at  the  different  par- 
allels. What  will  be  the  parallels  which  characterize 
the  different  colors  ?  M.  de  Boucheporn  immediately 
searches  for  those  which  offer  remarkable  peculiarities, 
those  whose  trigonometrical  lines,  the  sines  and  cosines, 
have  the  most  definite  relations  with  unity.  He  finds 
eight,  and  he  assigns  to  each  of  them  one  of  the  tints 
of  the  spectrum,  the  red  being  placed  at  the  equator. 
In  this  manner  he  draws  up  the  following  table,  in 
which  \h.Q.cosines  of  the  latitudes  selected  will  be  found 
opposite  to  the  tints  which  are  attributed  to  them  :  — 


SOUND   AND    LIGHT.  83 

Cosines  of  the 

Solar  Latitudes. 
t 

Violet,  .        .        .        .        .         .         .     0.33 

Indigo, 0.50 

Blue, 0.60 

Green, 0.70 

Yellow^  .         .         .         .         .         .         .0.80 

Orange  yellow,  f  Fresnel  had  taken  these  two"!    •      O.8/ 
Orange  red,        \instead  of  the  orange  alone.  J    m      O.Q3 

Red, i. oo 

It  is  next  to  be  ascertained  whether  these  numeri- 
cal values  are  proportional  to  the  length  of  the  waves, 
the  determination  of  which  has  been  made  by  Fresnel 
with  such  admirable  precision.  M.  de  Boucheporn 
observes  here  in  his  hypothesis,  that  the  experimental 
values  of  Fresnel  represent  the  sum  of  two  effects  ; 
the  progressive  motion  of  the  sun  exercises  a  friction 
as  well  as  its  rotation.  The  first  of  these  two  effects 
may  be  eliminated  by  cancelling  a  constant  number 
in  the  values  given  by  Fresnel,  and  then  these  values 
take  the  following  form,  the  length  of  the  red  wave 
being  taken  for  unity  :  — 

Lengths  of  Undulation. 

Violet, 0.396 

Indigo,       .         .         .         .         .         .         .     0.518 

Blue,  ....     0.600 


84         UNITY  OF  NATURAL  PHENOMENA. 

Lengths  of.  Undulation. 

Green, 0.696 

Yellow, 0.800 

Orange  yellow,           .         .        .        .        .  0.865 

Orange  red, ,  0.932 

Red,           .        .        .        .        .        .        .  i.ooo 

If  the  two  numerical  series  which  precede  be  com- 
pared with  each  other,  there  will  be  found  between 
them  the  most  perfect  harmony  that  could  be  asked 
for  experimental  calculations. 

The  views  of  M.  de  Boucheporn  present  a  striking 
aspect,  if  we  consider  the  three  principal  colors  of  the 
solar  spectrum,  the  blue,  the  yellow,  and  the  red,  which 
are  alone  able  to  make  white  light  without  the  aid  of 
the  intermediate  tints.  For  these  three  fundamental 
colors,  the  values  expressed  in  the  two  series  are  ex- 
actly as  the  numbers  3,  4,  and  5  ;  and  not  only  do  these 
numbers  present  a  very  simple  relation  to  each  other, 
but  they  are  also  the  only  ones  which  satisfy,  in  a 
simple  manner,  another  characteristic  condition  :  the 
square  of  one  of  them  is  equal  to  the  sum  of  the 
squares  of  the  other  two  :  9  +16  =25.  This  is  what 
M.  de  Boucheporn  calls  the  law  of  the  three  squares. 
It  takes  a  prominent  part  in  his  theories,  and  we 
cannot  help  appreciating  its  importance.  The  motions 
which  strike  our  senses  are  the  better  grouped  the 


SOUND   AND    LIGHT.  85 

more  simple  are  the  numbers  which  express  them  ;  at 
the  same  time  the  intensity  of  our  sensations  is  in  a 
direct  ratio  with  the  squares  of  these  numbers.  Our 
senses,  then,  are  called  upon  to  judge  of  the  double 
condition  which  is  fulfilled  when  these  numbers  and 
their  squares  present  such  very  simple  relations.  We 
can  here  see,  with  M.  de  Boucheporn,  one  of  the  har- 
monies of  Nature. 

The  general  explanation  that  has  just  been  given 
upon  the  subject  of  the  transversal  motion  of  light 
will  doubtless  be  regarded  as  but  a  brilliant  flight  of 
fancy,  and  our  chief  object  in  mentioning  it  has  been 
to  justify  the  judgment  we  passed  at?  the  beginning  of 
this  essay  upon  M.  de  Boucheporn's  book.  On  the 
other  hand,  the  hypothesis  of  the  rotation  of  atoms 
which  we  have  borrowed  from  Father  Secchi,  is  a 
very  plausible  and  suggestive  one,  and  it  would  be 
necessary  to  be  on  one's  guard  against  putting  the 
two  conceptions  upon  the  same  footing. 

Whatever  may  be  the  reason  assigned  for  the  trans- 
versal motion  of  the  luminous  wave,  the  fact  itself  is 
certain.  It  has  been  fully  proved  by  the  phenomena 
of  polarization. 

When  a  ray  of  a  single  color,  a  red  ray,  for  example, 
is  reflected  by  a  plate  of  glass  at  an  angle  of  thirty- 
six  degrees,  it  acquires  from  this  single  circumstance 


86  UNITY    OF   NATURAL    PHENOMENA. 

peculiar  properties.*  If  to  this  reflected  ray  a  second 
mirror  of  glass  be  presented  at  the  same  angle  of 
thirty-six  degrees,  and  the  mirror  is  made  to  turn  in 
every  direction  around  the  point  of  incidence,  it  is 
observed  that  the  ray  is  no  longer  reflected  with  the 
same  intensity  in  all  directions.  There  is  a  plane  in 
which  the  reflection  is  greatest,  and  one  in  which  it 
is  almost  nothing.  The  maximum  takes  place  in  the 
plane  parallel  to  the  plane  of  reflection  upon  the  first 
mirror,  and  is  consequently  called  the  plane  of  polari- 
zation ;  the  minimum  occurs  in  the  plane  which 
makes  a  right  angle  with  this.  If,  instead  of  selecting 
a  ray  of  a  particular  color,  just  as  now  mentioned,  we 

*  When  a  luminous  beam  impinges  at  the  proper  angle  on  a 
plane  glass  surface,  it  is  polarized  by  reflection.  It  is  polarized, 
in  part,  by  all  oblique  reflections,  but  at  one  particular  angle  the 
reflected  light  is  perfectly  polarized.  An  exceedingly  beautiful 
and  simple  law,  discovered  by  Sir  David  Brewster,  enables  us 
readily  to  find  the  polarizing  angle  of  any  substance  whose  re- 
fractive index  is  known.  This  law  was  discovered  experimental- 
ly by  Brewster,  but  the  Wave  Theory  of  light  renders  a  Complete 
reason  for  the  law.  A  geometrical  image  of  it  is  thus  given : 
When  a  beam  of  light  impinges  obliquely  upon  a  plate  of  glass, 
it  is  in  part  reflected  and  in  part  refracted.  At  one  particular 
incidence  the  reflected  and  the  refracted  portions  of  the  beam  are 
at  right  angles  to  each  other.  The  angle  of  incidence  is  then  the 
polarizing  angle.  It  varies  with  the  refractive  index  of  the  sub- 
stance, being  for  water  52^°,  for  glass  57^°,  and  for  diamond  68°. 
—  Fragments  of  Science,  p.  257. 


SOUND   AND   LIGHT.  87 

employ  white  light,  we  obtain  similar  results,  only  a 
little  less  distinct,  because  the  angle  of  incidence  un- 
der which  they  are  produced  varies  a  little  for  the 
different  colors. 

What  is,  then,  this  modification  which  the  ray  un- 
dergoes when  placed  in  the  conditions  we  have  men- 
tioned ?  Why  does  it  no  longer  behave  like  an  ordi- 
nary ray  ?  The  transverse  vibration  furnishes  us  with 
the  reason.  Before  the  luminous  beam  falls  upon  the 
first  reflector,  the  waves  are  propagated  around  it 
transversally  in  all  directions.  They  diverge  around 
this  axis  as  the  spokes  of  a  wheel  go  out  from  the 
hub.  At  the  moment  of  its  falling  upon  the  mirror, 
the  glass  absorbs  one  portion  of  the  waves  and  re- 
flects the  other.  What  are  chiefly  the  ones  it  sends 
back  ?  Those  which  are  parallel  to  its  surface,  and 
therefore  which  can  less  easily  penetrate  it.  If  we  go 
to  extremes  in  order  to  render  the  phenomena  more 
intelligible,  we  shall  consider  the  reflected  ray  as  no 
longer  containing  other  than  parallel  waves  between 
them  and  the  surface  of  the  first  mirror.  The  ray, 
then,  is  said  to  be  polarized,  and  this  term,  though 
invented  by  Newton  for  an  altogether  different  hy- 
pothesis, explains  sufficiently  well  the  fact.  What  will 
now  happen  when  these  waves,  conducted  in  a  single 
direction,  shall  fall  upon  a  second  surface  of  glass  ? 


88        UNITY  OF  NATURAL  PHENOMENA. 

They  will  be  wholly  reflected  at  the  moment  that  the 
mirror  is  parallel  to  them,  and  they  will,  on  the  other 
hand,  be  absorbed  more  and  more  in  proportion  as 
this  mirror  is  made  to  revolve.  Such  is,  in  its  essence, 
the  phenomenon  of  polarization,  and  it  appears  that  it 
may  be  explained  without  difficulty,  by  taking  for  the 
starting-point  the  transversal  undulation. 

Fresnel  has  even  shown  that  if  two  rays,  polarized 
at  right  angles,  happen  to  coincide,  they  give  no  sign 
of  interference,  even  when  there  is  between  them  the 
difference  of  a  half  undulation.  This  will  be  under- 
stood by  recurring  to  the  fundamental  notion  of  inter- 
ferences, and  it  will  not  be  a  matter  of  astonishment 
that  vibrations,  when  they  are  perpendicular  to  each 
other,  do  not  destroy  each  other,  as  happens  in  other 
cases. 

If  we  could  push  this  investigation  a  little  farther, 
we  should  be  able  to  show  how  the  data  assumed  in 
the  matter  of  luminous  motion  have,  one  after  another, 
received  striking  confirmation.  The  principles  being 
laid  down,  mathematical  analysis  has  developed  their 
consequences,  and  observation  has  justified  these  re- 
sults. In  pursuing  this  twofold  task  Fresnel  made 
for  himself  a  glorious  name.  His  calculations,  his 
experiments,  are  alike  memorable ;  one  hardly  knows 
what  most  to  admire,  the  high  intelligence  with  which 


SOUND   AND    LIGHT.  89 

he  has  presented  the  facts,  or  the  practical  skill  with 
which  he  has  verified  them.  In  no  other  portion  of 
science  has  man  so  nearly  arrived  at  the  secrets  of 
nature,  or  submitted  its  fundamental  phenomena  to 
such  exact  measurements. 


IV. 


What  does  the  Study  of  Light  teach  us  concerning  the 
Molecular  Constitution  of  Bodies  ? 

IN  pointing  out  some  of  the  laws  of  optics,  we  have 
endeavored  to  give  form  and  substance  to  the  notion 
of  ether.  It  has  been  seen  how  the  motions  of  this 
fluid  have  been  analyzed  and  measured.  It  has  been 
seen  that  the  ether,  notwithstanding  its  imponderabili- 
ty, possesses  the  properties  of  matter.  Henceforward, 
if  we  resume  the  thread  which  is  to  guide  us,  if  we 
place  ourselves  at  the  stand-point  from  which  all  phys- 
ical phenomena  appear  as  exchanges  of  motions,  we 
are  led  to  ask  if  it  has  been  possible  to  precisely  de- 
fine the  conditions  under  which  the  atoms  of  the  ether 
exchange  their  motions  with  the  ponderable  mole- 
cules. Diffused  throughout  the  stellar  spaces,  enclos- 
ing among  its  particles  the  celestial  globes,  the  ether 
thus  penetrates  into  the  deepest  recesses  of  all  bodies, 


QO        UNITY  OF  NATURAL  PHENOMENA. 

and  bathes  their  ultimate  molecules.  Thus  there  is 
no  phenomenon  in  which  it  does  not  play  a  part,  either 
the  principal,  or,  at  least,  a  secondary  one.  If,  then, 
we  could  know  the  mass  and  velocity  of  the  ethereal 
atoms,  and  the  mass  and  the  velocity  of-  the  ponder- 
able molecules,  we  should  possess,  in  some  sort,  the 
key  to  the  physical  sciences.  He,  at  least,  who  should 
discover  some  bond  of  union  between  these ;  who 
should  be  able  to  grasp,  in*  some  degree,  their  rela- 
tion ;  such  a  one  would  open  up  a  fruitful  source  of 
discoveries. 

Is  there  need  to  say  it  ?  No  such  discovery  has 
been  made  up  to  the  present  time.  We  establish  by 
the  results  the  reciprocal  action  of  ether  and  of  ordi- 
nary matter,  we  see  an  incandescent  body  produce 
light,  we  see  this  light  converted  into  chemical  action  ; 
but  in  no  instance  do  we  know  how  to  reduce  the 
phenomenon  to  its  mechanical  elements,.and  to  seize 
the  moment  itself  of  the  exchange  of  motion. 

In  regard  to  the  distances  themselves  of  the  atoms 
from  each  other  and  of  the  molecules  from  each  other, 
we  have  only  rough  and  contradictory  estimates.  It 
is  generally  supposed  that  the  spaces  left  between  the 
ponderable  molecules  are  enormous  in  proportion  to 
their  dimensions.  Thomas  Young  did  not  hesitate  to 
affirm  that  the  molecules  of  water  are  placed  in  rela- 


SOUND   AND    LIGHT.  9 1 

tion  to  each  other  as  if  a  hundred  men  were  equally 
distributed  over  the  whole  area  of  England,  that  is 
to  say,  distant  from  each  other  thirty  English  miles. 
Nevertheless,  crystallographers  are  far  from  believing 
in  such  considerable  spaces.  As  far  as  ether  is  con- 
cerned, Cauchy  has  deduced,  from  very  delicate  calcu- 
lations, that  the  distance  of  the  atoms  approximates 
to  the  two  hundredth  part  of  the  red  wave  :  according 
to  this,  there  would  be  three  hundred  thousand  atoms 
in  the  length  of  a  millimetre.  M.  de  Boucheporn,  on 
his  side,  believes  he  can  affirm  that  the  ethereal  atoms 
are  crowded  together  to  such  a  degree  that  the  sum 
of  the  empty  spaces  is  reduced  to  the  twentieth  part 
of  the  sum  of  those  filled  by  the  atoms.  In  conclu- 
sion, these  problems  remain  intact,  and  their  solution 
has  not  even  been  approached. 

It  would  seem  that  the  light  which  passes  through 
bodies  ought  to  give  us  information  in  regard  to  the 
molecular  spaces. 

There  are  transparent  substances,  the  molecules  of 
which  permit  the  luminous  waves  to  pass  freely,  with- 
out losing  any  part  of  their  motion.  Among  trans- 
parent bodies,  a  certain  number  are  colored  ;  they 
arrest  or  absorb  the  waves  of  certain  colors  only. 
Thus  a  solution  of  sulphate  of  copper  allows  the  blue 
waves  to  pass,  and  stops  the  red  rays  ;  if  there  be 


92        UNITY  OF  NATURAL  PHENOMENA. 

projected  upon  the  screen  through  this  solution  a 
spectrum,  the  red  end  of  the  spectrum  is  entirely  cut 
off.  A  piece  of  red  glass,  on  the  other  hand,  owes  its 
color  to  the  fact  that  its  substance  may  be  freely 
traversed  by  the  red  waves,  while  the  shorter  waves 
become  extinguished  in  it ;  if  it  be  placed  in  the  path 
of  a  luminous  beam,  the  spectrum  is  reduced  to  a 
band  of  lively  red.  If  there  be  placed,  at  the  same 
time,  in  the  path  of  the  beam  the  solution  of  sulphate 
of  copper  and  the  piece  of  red  glass,  these  two  trans- 
parent bodies  extinguish  all  the  rays  at  once,  and 
produce  a  complete  opacity.  Some  other  body,  a 
solution  of  permanganate  of  potash,  for  example,  will 
extinguish  at  the  same  time  the  red  and  the  blue  rays, 
and  give  passage  only  to  the  yellow,  which  constitute 
the  central  portion  of  the  spectrum. 

Different  bodies,  then,  exercise  in  relation  to  lumi- 
nous waves  a  sort  of  power  of  election,  extinguishing 
some,  permitting  others  to  pass.  Here  it  is  the  long- 
est, there  the  shortest,  which  are  arrested  ;  in  other 
cases  both  the  longest  and  the  shortest  are  stopped 
at  the  same  time,  while  those  only  of  medium  length 
can  obtain  a  passage.  Whence  comes  this  differ- 
ence ?  What  law  presides  over  this  sort  of  select 
choosing  on  the  part  of  the  luminous  rays  ?  No 
doubt  it  arises  from  the  form  of  the  molecules,  and 


SOUND    AND    LIGHT.  93 

the  nature  of  their  motions.  We  are  hardly  able  to 
say  more  about  it.  The  difficult  molecular*  motions 
seem  to  have  rhythmical  periods  peculiar  to  each,  in 
virtue  of  which  they  come  into  harmony  with  those 
of  the  ethereal  atoms. 

That  there  should  thus  be  in  molecular  motions  a 
kind  of  rhythm,  from  which  results  the  selection  of 
colors,  has  been  demonstrated  in  a  general  manner  by 
the  study  of  the  spectrum  ;  but  there  may  be  men- 
tioned in  this  connection  several  curious  and  charac- 
teristic facts,  which  have  been  pointed  out  in  the  last 
few  years. 

Project  upon  a  screen  the  spectrum  of  a  solid  body 
strongly  heated.  So  long  as  the  body  remains  incan- 
descent only,  so  long  as  its  molecules  are  not  freed 
from  the  bonds  of  cohesion,  the  spectrum  remains 
continuous  ;  there  are  seen  neither  dark  nor  bright 
lines  ;  the  waves  of  all  the  colors  and  of  all  the  inter- 
mediate shades  are  produced  at  the  same  time.  If 
the  body  be  heated  still  more,  it  passes  the  point  of 
incandescence,  and  enters  a  state  of  combustion  ;  then 
the  molecules  become  free,  at  least  for  a  moment. 
Then,  also,  the  bright  and  dark  lines  appear  in  the 
spectrum.  The  waves  are  consequently  re-enforced  in 
some  places,  and  weakened  in  others  ;  they  are  gov- 
erned by  a  new  law. 


94         UNITY  OF  NATURAL  PHENOMENA. 

That  it  is  the  molecules  themselves  of  the  heated 
body  which,  in  their  state  of  freedom,  impress  upon 
the  waves  these  peculiar  modifications,  cannot  be 
doubted,  for  every  substance  gives  in  this  manner 
lines  so  clear  and  definite  that  their  appearance  alone 
is  sufficient  to  distinguish  it. 

Acoustics  furnishes  us,  upon  the  subject  of  these 
phenomena,  with  analogies  which  present  themselves 
spontaneously  to  the  mind  ;  that  which  takes  place 
when  the  body  is  incandescent  may  be  compared  to 
the  noises  which  result  from  waves  mixed  up  and  of 
every  length ;  the  effects  produced  by  the  free  mole- 
cules remind  us  of  the  harmonious  sounds  emitted 
by  strings,  the  vibration  of  which  is  not  impeded  by 
any  obstacle. 

Here  is  also  a  new  fact  recently  discovered. 

We  have  just  seen  that  every  substance  in  burning 
gives  its  own  lines.  When,  for  example,  sodium  is 
burned,  a  very  bright  line  is  seen  in  the  yellow  por- 
tion of  the  spectrum,  in  a  clearly  marked  locality. 
(Line  D,  of  Fraunhofer.)  If,  now,  instead  of  burning 
sodium,  we  interpose  the  vapor  of  sodium  in  the  path 
of  the  ray  which  should  give  a  continuous  spectrum, 
the  phenomenon  is  completely  reversed  ;  at  the  exact 
point  where  just  now  there  was  a  bright  line,  a  dark 
line  appears.  Thus  the  vapor  of  sodium,  when  it  acts 


SOUND   AND   LIGHT.  95 

as  a  screen,  absorbs  exactly  those  rays  which  it  emits 

"  i 
when  it  acts  as  the  luminous  source. 

This  fact  observed  in  the  case  of  the  vapors  of 
iodine,  of  strontium,  and  of  iron,  has  become  gener- 
alized ;  it  is  now  known  under  the  name  of  the  re- 
versement  of  the  spectrum  ;  it  shows  that  bodies 
tend  at  the  same  time  to  absorb  and  to  emit  the 
same  waves. 

Shall  we  be  astonished  at  this  double  tendency, 
viewed  from  our  present  stand-point,  and  shall  we 
not  recognize  in  it  the  necessary  consequence  of  the 
principles  which  explain,  in  our  opinion,  all  physical 
science  ?  From  the  moment  that  certain  ethereal 
motions  have  a  special  facility  of  becoming  converted 
into  certain  molecular  motions,  these  latter  must  also 
easily  undergo  the  opposite  conversion.  The  recipro- 
city of  the  motive  forces  insures  to  us  that  of  thd 
phenomena. 

If  the  natural  bond  of  union  of  all  the  facts  we 
have  mentioned  be  sought  for,  it  will  be  seen  that, 
taken  together,  those  facts  come  to  the  support  of  that 
grand  law  we  have  endeavored  to  expound,  and  which 
we  have  designated  under  the  name  of  the  Unity  of 
the  Physical  Forces  ;  but  there  will  at  the  same  time 
be  observed  the  defects  in  the  method  we  are  obliged 
to  employ.  Were  we  dealing  with  a  system  ready- 


96        UNITY  OF  NATURAL  PHENOMENA. 

made,  we  might  unfold  it  step  by  step,  and  pass  from 
one  part  to  another  without  a  gap.  Far  from  this, 
we  have  to  do  with  a  system  seen  only  in  glimpses, 
scarcely  sketched,  even,  the  elements  of  which  are  so 
incomplete  as  to  be  found  insufficient,  it  may  be. 
Such  being  the  case,  what  remains  for  us  to  do,  if  not 
to  show  some  parts  brightly  illuminated,  while  leav- 
ing in  the  shade  whatever  is  obscure  ?  From  those 
scattered  lights,  these  fugitive  glimmerings,  must  re- 
sult the  conception  of  the  whole. 

The  digression  we  have  just  made  with  reference  to 

acoustics  and  optics  has  exhibited  to  us  the  branches 

• 
of  science  in  which  the  phenomena  of  motion  have 

been  best  studied — that  motion  which  we  now  see  un- 
derlying all  things.  Sonorous  motions,  luminous  mo- 
tions, have  been  verified,  measured,  and  scrutinized 
in  all  their  modes ;  but,  on  the  other  hand,  their  me- 
chanical effects  have  scarcely  been  glanced  at.  The 
study  of  heat  will  afford  a  contrary  result ;  heat-mo- 
tions are  at  the  most  suspected  only,  and  continue  to 
be  but  little  known  as  regards  their  real  nature  ;  but 
their  mechanical  effects  have  been  demonstrated  by 
splendid  experiments,  and  measured  with  the  utmost 
precision. 

Sound  and   light  on  one  side,  heat  on  the  other  : 
here  are  two  subjects  of  study,  as  yet  incompletely 


SOUND    AND    LIGHT.  9/ 

explored  ;  but  these  two  studies  complement  each 
other,  and  as  soon  as  we  approach  t*hem  we  see  shi- 
ning brightly  forth  that  idea  by  virtue  of  which  Nature 
appears  to  us  but  as  a  system  of  mutually  exchanging 
motions. 

It  is  from  comparisons  of  this  sort  that  our  thesis 
derives  its  principal  strength.  This  is  what  our  read- 
ers must  never  lose  sight  of  while  we  continue  to 
confront  the  system  of  the  unity  of  the  physical  forces 
with  facts  which  experience  has  acquainted  us  with. 
7 


98        UNITY  OF  NATURAL  PHENOMEN-A. 


CHAPTER   III. 
HEAT. 

I. 

The  Dynamic  Theory  and  Mechanical  Equivalent  of 
Heat. 

THE  theory  which  reduces  the  physical  world  to 
matter  and  motion,  presents  an  external  so  attractive 
as  to  provoke  a  sort  of  mistrust.  Accustomed  as  we 
are  to  complicated  appearances,  we  are  astonished  at 
this  pretentious  unity.  We  ask,  with  uneasiness,  if  we 
are  not  the  dupes  of  a  desire  to  simplify  everything. 
Is  not  this  hypothesis,  which  gives  us,  in  a  manner,  an 
insight  into  the  whole  plan  of  Nature,  a  deceitful  mi- 
rage? Are  we  not  deluded  by  fallacious  generaliza- 
tions ?  Are  we  not  enticed  into  falsifying  the  phe- 
nomena for  the  sake  of  forcing  them  to  enter  into  the 
frame  of  a  preconceived  theory  ?  To  these  questions 
a  reply  can  be  made  only  by  an  examination  of  the 
facts,  and  for  this  purpose  we  have  taken  a  brief  sur- 
vey of  the  different  provinces  of  physics. 


HEAT.  99 

The  natural  sequence  of  this  worl^  brings  us  now 
to  investigate  heat,  and  we  thus  find  ourselves  led  to 
discoveries  which  have  served  as  the  origin  of  the 
theory  of  the  unity  of  the  physical  forces. 

Here  our  task  becomes  easy,  perhaps,  but,  it  must 
also  be  added,  somewhat  thankless.  The  equiva- 
lence of  heat  and  mechanical  work  has  beeri  for  some 
years  past  not  a  new  idea ;  books,  public  instruction, 
and  lectures,  have  spread  it  abroad  ;  the  popular  mind 
has  been  zealously  informed  of  it.  We  have  not  to 
fear,  then,  that  the  subject  will  be  a  strange  one  to  our 
readers,  or  fear,  rather,  lest  they  have  heard  too  much 
of  it,  and  that  they  regard  it  as  commonplace.  We 
shall  then  only  recall,  very  briefly,  the  principles  of 
thermo-dynamics,  and  we  shall  strive  more  especially 
to  throw  light  upon  the  consequences  that  may  be 
drawn  from  them  as  regards  the  constitution  of 
bodies. 

Let  us  mention,  in  the  first  place,  a  book  which  pre- 
sents in  a  distinct  and  agreeable  form  all  the  essential 
data  of  the  new  theory  of  heat.  It  contains  twelve 
lectures,  delivered  by  Mr.  John  Tyndall,  at  the  Royal 
Institution,  London,  upon  Heat,  considered  as  a  Mode 
of  Motion.  The  course  was  delivered  in  1862 ;  the  book 
appeared,  in  France,  translated  by  the  Abb6  Moigne, 
in  1864,  and  it  was  immediately  appreciated  at  its  true 


IOO       UNITY  OF  NATURAL  PHENOMENA. 

value  by  all  persons  who  are  interested  in  the  general 
advancement  of  science.  It  is  impossible  to  give  to 
lessons  in  physics  a  greater  charm,  and,  at  the  same 
time  clearness,  than  has  been  done  by  Mr.  Tyndall 
in  the  work  we  name.  The  book  has  preserved  the 
form  of  oral  instruction ;  we  follow  the  words  and 
gestures  of  the  professor  ;  we  assist  in  the  details, 
even  in  the  very  mishaps  of  the  experiments.  It  must 
not  be  thought,  however,  that  we  have  before  us  an 
impromptu  effort  reproduced  by  the  art  of  the  stenog- 
rapher. Much  skill  lies  concealed  under  this  appar- 
ently easy  method  of  procedure.  Mr.  Tyndall  skil- 
fully calculates  all  his.  results ;  the  accidents  in  his 
experiments  occur  only  when  well  foreseen ;  they  are 
fortunate  mishaps  that  take  place  only  when  he  wishes 
to  seize  the  attention  of  his  public,  whether  listeners 
or  readers,  and  abruptly  direct  their  thoughts  to  some 
striking  anomaly. 

The  experiments  of*Mr.  Tyndall  are,  moreover,  con- 
ceived with  much  skill  and  ability.  For  a  long  time 
he  has  been  a  master  in  the  art  of  lecturing  before 
a  numerous  audience.  He  has  contrived  ingenious 
instruments  to  magnify  the  results  of  experiments. 
He  was  one  of  the  first  to  employ  the  electric  light 
for  projecting  on  screens  the  enlarged  images  of  the 
most  delicate  phenomena.  The  dramatic  effects  which 


HEAT.  IOI 

jj,j*j     j  >J»/ 

have  made  the  success  of  Mr.  TyiisBali$\ lectures,  a'p-; 
pear  adroitly  preserved  in  his  book.-1J  ,*  -  ;  r';'-  ^  ^ 

As  to  the  substance  of  these  lectures,  the  professor 
treats  his  subject  bit  by  bit ;  he  takes  his  time  to  pro- 
duce in  the  minds  of  his  pupils  those  ideas  which  the 
regenerated  study  of  heat  awakens. 

"  Remember,"  said  he  to  them,  "  we  are  entering  a 
jungle,  and  must  not  expect  to  find  our  way  clear. 
We  are  striking  into  the  branches  in  a  random  fashion 
at  first ;  but  we  shall  thus  become  acquainted  with  the 
general  character  of  our  work,  and,  with  due  persis- 
tence, shall,  I  trust,  cut  through  all  entanglement  at 
last."  When  he  has  sketched  the  principle  of  a  new 
conception,  "  Do  not  be  disheartened,"  he  makes  haste 
to  say,  "if  this  reasoning  shoujd  not  appear  quite 
clear  to  you.  We  are  now  in  comparative  darkness, 
but  as  we  proceed  light  will  gradually  appear,  and 
irradiate  retrospectively  our  present  gloom."  And,  in 
another  place,  "Whenever  a  difficult  expedition  is 
undertaken  in  the  Alps,  the  experienced  mountaineer 
commences  the  day  at  a  slow  space,  so  that  when  the 
real  hour  of  trial  arrives,  he  may  find  himself  hard- 
ened instead  of  exhausted  by  his  previous  work.  We, 
to-day,  are  about  to  enter  on  a  difficult  ascent,  and  I 
propose  that  we  commence  it  in  the  same  spirit ;  not 
with  the  flush  of  enthusiasm,  which  the  necessity  of 


IO2        UNITY  OF  NATURAL  PHENOMENA. 

"•labor  extinguishes,  but  with  patient  and  determined 
"?ic3rts»  vvhfichj  will  tfot  recoil  should  a  difficulty  arise." 
The  professor  conforms  in  every  particular  to  his  ex- 
cellent programme,  and  employs  a  good  deal  of  skill 
in  preparing  his  pupils  for  the  abstract  notions  he 
wishes  to  impart  to  them. 

Nevertheless  we  cannot  refrain  from  adding  that  the 
conclusions  of  the  book  remain  vague  and  unsatis- 
factory. 

We  are  acquainted  with  the  history  of  the  works, 
and  of  the  discoveries  which  successively  modified 
and  defined  the  idea  of  heat. 

As  in  the  case  of  light,  two  theories  for  a  long  time 
confronted  each  other :  that  which  made  of  heat  a 
material  substance,  and  that  which  saw  in  it  only  a 
mode  of  motion.  The  material  nature  of  caloric  con- 
tinued to  be  admitted  much  later  than  that  of  light. 
During  the  latter  years  of  the  eighteenth  century, 
Lavoisier  and  Laplace,  in  presenting  to  the  Academy 
of  Sciences  a  memoir  compiled  in  common,  upon  the 
subject  of  heat,  seemed  to  hold  the  balance  equally 
between  the  two  opinions.  Their  language  was,  "We 
shall  not  decide  between  the  two  foregoing  hypothe- 
ses ;  several  phenomena  would  seem  to  favor  the  lat- 
ter (that  of  motion),  as,  for  example,  the  heat  pro- 
duced by  the  rubbing  together  of  two  solid  bodies ; 


HEAT.  IO3 

but  there  are  others  which  are  more,  simply  explained 
by  the  first  (that  of  its  material  nature)  ;  perhaps  both 
obtain  at  once." 

In  reality  they  abandoned  the  idea  of  motion  with- 
out having  made  any  use  of  it,  and  returned  to  the 
theory  of  the  material  nature  of  heat.  Laplace,  espe- 
cially, after  the  termination  of  his  connection  with 
Lavoisier,  became  a  confirmed  supporter  of  this  last 
theory,  which  was  thus  strengthened  by  a  weighty 
authority. 

A  little  later,  during  the  last  years  of  this  century, 
Rumford,  an  original,  almost  paradoxical  mind,  reso- 
lutely pronounced  himself  against  the  materiality  of 
heat.  "  If  heat,"  he  said,  "  is  a  matter  lodged  in  the 
pores  of  different  substances,  it  may  be  forced  out,  as 
water  is  squeezed  from  a  sponge,  and  the  same  body 
will  not  be  able  to  emit  it  indefinitely."  Having  thus 
brought  the  question  to  a  decisive  experiment,  he 
caused  an  iron  bar  to  turn  upon  another  similar  bar 
in  the  midst  of  a  liquid,  and  he  showed  that  there  was 
a  disengagement  of  heat  as  long  as  the  iron  bar  was 
turning. 

The  experiments  of  Rumford  had  not  as  much 
.celebrity  as  they  deserved.  Thomas  Young  alone 
seemed  to  understand  their  bearing.  In  a  treatise 
upon  physics,  published  in  1807,  he  exhibited  the 


104       UNITY  OF  NATURAL  PHENOMENA. 

labors  of  Rumford,  and  compared  them  with  his  own 
discoveries  in  regard  to  heat ;  but  the  old  ideas  upon 
caloric  continued  to  hold  their  sway  in  men's  minds. 

Steam  engines  came,  and  all  the  questions  pertain- 
ing to  heat  again  became  the  order  of  the  day.  At 
this  time  the  materiality  of  heat  was  so  little  disputed 
that  Sadi  Carnot  took  it  as  the  basis  of  his  celebrated 
Reflections  on  the  Motive  Power  of  Fire  (1824).  It 
is  known  how,  starting  from  this  erroneous  doctrine, 
Sadi  Carnot,  and  his  celebrated  commentator,  Clapey- 
ron,  revived  the  thermo-dynamic  theory.  They  called 
attention  to  the  causes  which  enabled  an  engine  burn- 
ing charcoal  in  its  furnace  to  produce  work  at  its  shaft. 
They  had  this  good  fortune,  that  their  arguments  — 
their  formulas,  even  —  could  be  disengaged  from  the 
fundamental  error  which  contaminated  them,  and  serve 
as  a  basis  for  the  new  theory  of  heat. 

In  1839  M-  Seguin  published  an  Essay  on  the  Influ- 
ence of  Railroads.  In  it  heat  was  considered  as  a 
motion,  and  the  author  gave  very  appropriate  hints 
concerning  the  transformation  of  this  motion  into 
work  ;  but  this  subject  was  but  touched  upon  in  the 
book  of  M.  Seguin,  who  had  particularly  in  view 
questions  of  social  economy. 

* 

Between  the  years  1840  and  1850  were  produced 
the  remarkable  works  of  M.  M.  Mayer  and  Joule. 


HEAT.  IO5 

Starting  from  very  different  premises,  and  placed  at 
totally  different  stand-points,  —  tl\e  one  in  Germany, 
the  other  in  England,  —  they  came  at  the  same  time 
to  clearly  demonstrate  the  equivalent  of  heat  and 
mechanical  work,  and  they  determined  the  ratio  of 
this  equivalence. 

Immense  result !  It  was  like  a  shining  beacon 
lighted  up  in  the  midst  of  the  darkness  which  en- 
shrouded physical  science  when  this  definite  fact  was 
made  known.  A  unit  of  heat  is  equivalent  to  four 
hundred  and  twenty-five  kilogrammetres,  or,  in  other 
words,  the  quantity  of  heat  which  is  required  for  ele- 
vating one  degree  the  temperature  of  a  kilogramme 
of  water,  can  also  do  the  work  which  consists  in  ele- 
vating four  hundred  and  twenty-five  kilogrammes  to 
the  height  of  one  metre. 

This  discovery  has  for  fifteen  years  vastly  increased 
the  field  of  vision  for  science.  There  springs  from  it, 
as  it  were,  a  new  philosophy  of  nature.  A  mental 
revolution  is  taking  place,  of  which  we  see  only  the 
commencement,  and  we  are  endeavoring  to  sketch  the 
beginnings  of  this  change. 

All  uncertainty  in  regard  to  the  nature  itself  of  heat 
came  to  an  end  as  soon  as  its  mechanical  equivalent 
had  been  determined.  What  is  it  that  could  be  trans- 


IO6       UNITY  OF  NATURAL  PHENOMENA. 

formed  into  motion  in  so  regular  a  manner  if  it  be  not 
another,  motion  ? 

Doubtless  there  would  not  be  discovered  at  once, 
either  in  the  action  of  steam  engines,  or  any -other 
phenomena,  the  precise  mode  of  the  transformation  ; 
but  the  principle  of  it  was  grasped  by  the  mind  with 
conviction.  The  motion  itself  was  not  seen,  but  its 
effects  were  both  perceived  and  measured. 

Heat  is  a  motion  ;  but  of  what  kind  ? 

Some  physicists  conceived  at  first  that  it  might  be 
due  to  the  longitudinal  vibrations  of  the  ether.  They 
knew  that  ether,  by  its  transversal  vibrations,  pro- 
duced light.  With  regard  to  the  longitudinal  action, 
that  which  is  produced -in  the  direction  of  the  ethereal 
ray,  no  especial  property  was  known,  and  they  dis- 
posed of  it  by  attributing  to  it  the  calorific  effects. 
This  conjecture,  which  did  not  rest  upon  any  well- 
grounded  fact,  has  gathered  around  it  but  a  very  small 
number  of  supporters,  and  has  scarcely  been  consid- 
ered more  than  a  work  of  the  imagination. 

According  to  present  notions,  heat  is  a  motion  of 
the  molecules  themselves  of  bodies.  All  material 
molecules  are  endued  writh  this  motion  ;  they  strike, 
without  cessation,  against  each  other,  and  thus  main- 
tain or  change  their  state.  By  means  of  their  shocks 
the  molecules  of  bodies  cause  us  to  experience  the 


HEAT.  ID/ 

sensation  of  heat,  and  from  the  intensity  of  these 
shocks  we  determine  degrees  of  temperature.  This 
perpetual  vibration  of  the  molecules  itself  constitutes 
the  phenomenon  of  heat ;  but.it  may  naturally  convert 
itself  into  different  effects.  It  can,  when  circum- 
stances are  favorable,  agitate  the  ether,  and  produce 
light ;  it  can  agitate  the  air,  and  produce  sounds  ;  it 
may  concentrate  itself  in  order  to  move  masses,  and 
produce  what  has  very  properly  been  called  mechani- 
cal work. 

Properly  speaking,  the  different  effects  we  have  just 
mentioned  —  heat,  light,  sonorous  shock,  mechanical 
work,  and  other  effects  of  the  same  class,  which  we 
do  not  mention  at  this  time,  —  are  but  the  different 
manifestations  of  the  same  cause.  The  motion  with 
which  each  molecule  is  endowed  at  a  given  moment 
constitutes  for  it  a  sort  of  intrinsic  energy.  In  me- 
chanics we  are  able  to  appreciate  and  measure  the 
energy  with  which  a  moving  body  is  endowed.  The 
product  of  the  mass  of  a  body  into  the  square  of  its 
velocity  expresses  what  is  called  the  vis  viva,  or  living 
force.  This  product  has  not,  properly  speaking,  any 
physical  representation,  and  it  offers  to  the  mind  at 
first  a  conception  rather  abstract ;  but  it  assumes  a 
capital  importance  from  this  circumstance,  that  it  is 
equivalent  to  double  the  work  that  the  body  can  pro- 


IO8       UNITY  OF  NATURAL  PHENOMENA. 

duce  in  losing  all  its  velocity  ;  it  gives  then  the  meas- 
ure of  the  dynamic  effect  which  the  body  in  motion 
contains  within  it.  We  may  now  declare,  making  use 
of  this  idea,  that  all  particles  of  matter  possess,  at  a 
given  instant,  a  certain  amount  of  living  force.  They 
may  lose  •  a  portion  of  it  in  doing  some  work,  —  that 
is,  by  displacing  a  mass,  —  but  then  the  vis  viva  which 
they  lose  becomes  stored  up  in  the  work  performed, 
and  it  is  renewed  when  this  work  is  undone. 

Let  us  consider  a  steam  engine,  and  neglecting  all 
the  losses  of  force  or  work  which  belong  to  the  me- 
chanism itself,  let  us  think  only  of  the  theoretical  or 
ideal  action  of  the  engine.  The  steam  expands,  for- 
cing out  the  piston  ;  each  molecule  of  vapor  thus  loses 
a  certain  quantity  of  vis  viva.  These  accumulated 
losses  produce  a  revolution  of  the  shaft,  which  is  en- 
gaged, for  instance,  in  elevating  a  weight.  At  the  end 
of  the  operation  all  the  vis  viva  which  the  steam  has 
lost  is  virtually  found  in  the  elevated  weight.  If  I  cut 
the  cord  which  sustains  this  weight,  it  will  fall,  and  re- 
produce in  its  fall  all  the  vis  viva  which  has  been  ex- 
pended in  order  to  raise  it.  It  will  appear  in  the  form 
of  heat  at  the  instant  when  the  body  strikes  the 
ground,  and  if  this  could  be  collected  and  restored  to 
the  steam,  the  latter  would  be  replaced  in  the  condi- 


HEAT. 

tion  in  which  it  was  found  at  the  beginning  of  the 
operation.  , 

What  we  have  indicated  in  this  rough  example,  is 
constantly  taking  place  in  all  nature.  To  bring  the 
vis  viva,  or  living  force,  into  the  condition  of  work, 
and  then  to  reproduce  it,  in  this  lies  the  whole  activity 
of  Nature. 

II. 

Changes  of  State  produced  by  Heat  furnish  Informa- 
tion as  to  the  Constitution  of  Bodies. 

ADMITTING  an  incessant  agitation  of  the  molecules, 
it  is  easier  to  account  for  the  phenomena  which  take 
place  in  bodies  when  they  pass  from  the  gaseous  to 
the  solid  and  liquid  states. 

As  a  general  rule,  all  bodies  are  susceptible  of  these 
three  states  :  carbonic  acid  gas  has  been  liquefied  and 
solidified  ;  water  appears  to  us  under  the  form  of  ice 
and  vapor  ;  we  know  how  to  fuse  and  volatilize  the 
metals.  We  do  not  always  possess  sufficient  means 
for  making  every  body  pass  successively  through  these 
three  states  ;  but  we  may,  nevertheless,  affirm  that  we 
should  see  them  under  all  three  forms,  if  our  re- 
searches could  include  a  sufficiently  extended  scale 
of  temperatures. 


IIO       UNITY  OF  NATURAL  PHENOMENA. 

As  a  general  rule,  also,  it  may  be  said  that  heat  must 
be  increasingly  added  to  the  same  body  to  bring  it 
from  the  solid  to  the  liquid  state,  then  to  the  gaseous. 
Thus  heat  triumphs  over  the  bonds  which  bind  to- 
gether the  molecules ;  it  combats  those  attractive 
forces  which  manifest  themselves  in  the  interior  of 
bodies,  and  which  have  preserved  until  now  so  myste- 
rious an  aspect. 

Plas  it  been  possible,  through  the  antagonism  which 
is  displayed  between  heat  and  the  attractive  forces,  to 
isolate  the  calorific  motion  ?  to  separate  it  from  the 
phenomena  which  mask  it  ?  to  determine  its  special 
mode  and  laws  ?  Unfortunately  not.  Nevertheless  it 
may  be  said  that  the  study  of  gases  has  thrown  much 
light  upon  this  question. 

How  must  we  conceive  of  the  gaseous  state  ?  To 
begin  with,  it  is  characterized  by  a  considerable  dis- 
tance between  the  molecules.  Endued  with  a  great 
projectile  velocity,  these  molecules  hurl  themselves 
against  each  other,  or  against  the  bounds  of  the  space 
which  confines  them.  Have  they  merely  a  projectile 
motion  ?  They  have  necessarily  a  rotatory  motion 
also,  for,  if  this  motion  did  not  exist  at  a  given  mo- 
ment, it  could  not  fail  to  be  generated  by  the  incessant 
collisions  of  the  different  molecules.  The  eccentric 
shocks,  those  which  do  not  pass  through  the  centres 


HEAT.  Ill 

of  gravity,  are,  in  fact,  of  such  a  nature  as  to  produce 
a  rotation.  This  rotation  combines  with  their  elas- 
ticity to  cause  the  molecules  to  recoil  from  each  other. 
The  former  alone  might  produce  this  effect,  if  the 
molecules,  instead  of  being  compound,  were  but  sim- 
ple atoms.  A  sort  of  medium  state  is  thus  established 
in  the  gas.  If  the  motion  became  weak  at  certain 
points,  it  would  at  once  be  strengthened  by  the  agita- 
tion of  the  rest  of  the  mass.  Moreover,  each  mole- 
cule recoils  without  definite  direction,  and  may  go  in 
all  directions,  to  be  successively  projected  into  every 
part  of  the  entire  mass.  There  is  a  state  of  complete 
liberty. 

Let  us  observe  that  the  molecular  distances  are  con- 
siderable ;  their  velocities  are  also  considerable.  What 
becomes,  then,  of  that  effect  which  must  be  produced 
at  the  instant  when  two  molecules  approach  and  strike 
each  other,  that  effect  which  is  attributed  to  the  attrac- 
tive forces,  whatever  they  may  be  ?  This  effect  is,  so 
to  speak,  annulled  ;  it  lasts  only  a  very  short  time 
relatively,  since  the  molecular  distances  are  very  great. 
It  is  but  a  very  transient  effect,  since  the  velocities  are 
enormous.  It  becomes  so  weak  that  it  may  be  neg- 
lected ;  thus,  in  the  gases,  the  attractive  forces  possess 
no  power.  The  calorific  motion  exists  in  them  with- 
out antagonism,  and  may  be  observed  in  its  integrity. 


112        UNITY  OF  NATURAL  PHENOMENA. 

If  we  apply  cold  to  a  gas,  if  we  cause  it  to  lose  a 
portion  of  its  vis  viva,  the  energy  and  amplitude  of 
its  oscillations  will  gradually  diminish.  A  moment 
will  come  when  each  molecule  will  be,  as  it  were,  im- 
prisoned by  its  neighbors,  and  forced  to  oscillate  along 
a  limited  curve.  The  gas  will  have  become  a  liquid. 

From  the  very  fact  alone  of  the  proximity  of  the 
molecules  the  attractive  forces  have  regained  the  su- 
premacy, and  have  destroyed,  in  part,  the  mobility  of  the 
system.  Gravity,  too  weak  before,  now  makes  itself 
felt,  and  the  molecules  are  obliged  to  arrange  them- 
selves in  such  a  manner  as  to  present  a  surface  paral- 
lel to  the  horizon. 

Along  this  surface  they  are  detained  in  their  new 
position  by  one  of  their  sides  only  ;  upon  the  other 
side  their  motions  remain  free,  and  they  possess  an 
especial  aptitude  for  returning  to  their  former  state, 
and  an  evaporation  takes  place  from  the  surface. 

Moreover,  in  the  remainder  of  the  mass,  the  mole- 
cules still  enjoy  a  relative  amount  of  liberty.  They 
are  enclosed  within  restricted  orbits,  but  their  axes  of 
rotation  continue  to  lie  in  all  directions.  They  can 
thus  roll  over  each  other  to  some  extent. 

Besides,  the  bonds  which  limit  their  movement 
yield  to  the  slightest  effort,  and  the  whole  mass  may 
be  mixed  without  difficulty. 


HEAT.  113 

Let  us  continue  the  application  of  cold.  The  mole- 
cules approach  each  other  ;  they  enter,  one  may  say, 
within  the  sphere  of  each  other's  action,  and  they  re- 
main there  ;  their  axes  of  rotation  become  upright, 
and  take  a  common  direction  ;  the  body  has  passed 
into  the  solid  state. 

During  these  conditions  the  molecules  still  oscillate  ; 
but  they  can  no  longer,  without  outside  assistance,  de- 
part from  the  circle  in  which  they  are  kept  by  their 
neighbors. 

In  describing  the  manner  in  which  bodies  change 
their  state,  we  have  just  brought  forward  the  attrac- 
tive forces.  After  the  repeated  declarations  we  have 
already  made,  we  might  almost  forbear  to  mention 
that  these  forces  are  for  us  but  the  symbols  under 
which  lie  concealed  the  ordinary  phenomena  of 
motion. 

Before  terminating  this  work,  we  shall  be  brought 
to  consider  collectively  these  attractive  forces,  which 
we  admit  this  time  by  way  of  inventory.  Nevertheless, 
let  us  now  make  a  rapid  allusion  to  them,  so  as  not  to 
leave  them  entirely  in  mystery. 

It  is  a  necessary  consequence  of  the   rotation  of 

molecules  that  they  draw  with  them  into  their  motion 

a  certain  number  of  ethereal  atoms.     They  are  thus 

wrapped  in  a  sort  of  atmosphere  whose  radius  may 

8 


114       UNITY  OF  NATURAL  PHENOMENA. 

vary  according  to  circumstances,  and  which  nearly 
represent  that  which  we  just  now  called  the  molecular 
sphere  of  action.  So  long  as  these  atmospheres  do 
not  touch  each  other  there  is  no  action  ;  such  is  the 
case  with  gases.  If  the  molecules  approach  each 
other,  and  the  atmospheres  slide  over  each  other  (this 
is  the  case  with  liquids),  action  begins,  an  action 
purely  mechanical,  due  to  the  meeting  of  the  ethereal 
atoms.  If,  finally,  the  atmospheres  penetrate  more 
deeply  into  each  other,  the  effect  is  more  strongly 
pronounced ;  the  ethereal  envelopes  that  are  pene- 
trated find  themselves  hindered  in  their  progress,  and 
they  behave  so  as  to  render  parallel  the  rotations  of 
the  different  molecules  respectively,  as  happens  in 
the  case  of  solids. 

With  this  sketch,  let  us  pass  hastily  on,  as  we  are 
unwilling  to  delay,  in  order  to  speak  of  liquids  and 
solids,  the  constitution  of  which  continues  even  now 
very  obscure.  It  is  sufficient  that  we  have  shown  how 
the  laws  of  this  constitution  are  connected  with  those 
laws,  far  better  known,  which  govern  the  gaseous  state. 
Thanks  to  this  solidarity,  the  gases  offer  us  a  con- 
venient type  for  studying  molecular  motion,  and  we 
may  fix  our  attention  upon  them  some  moments 
longer,  sure  of  deriving  from  them  information  ap- 
plicable to  all  the  forms  of  matter. 


HEAT.  115 

III.     -, 

Theory  of  Gases. 

THE  theory  of  gases,  the  principle  of  which  was 
just  now  pointed  out,  has  been  much  studied  of  late 
years,  and  it  has  given  rise  to  a  great  number  of  re- 
markable publications.  It  does  not  present  itself, 
however,  as  an  entirely  novel  conception,  for  its  fun- 
damental notion  could  be  found  in  the  Hydrodynamics 
of  Bernouille,  published  in  1738  ;  but,  buried  in  the 
work  of  Bernouille,  it  scarcely  saw  the  light  until  the 
last  thirty  years,  and  it  has  received  its  development 
only  through  the  quite  recent  works  of  M.  Joule  and 
M.  Clausius. 

We  cannot  here  follow  those  two  physicists  in  the 
analytical  deductions,  by  means  of  which  they  have 
defined,  with  wonderful  accuracy,  the  theory  of  gases. 
But  we  shall  at  least  be  able  to  show  how  the  hy- 
pothesis in  regard  to  the  constitution  of  gases,  which 
we  have  just  sketched,  accounts  for  the  facts  succes- 
sively -revealed  by  experiment. 

From  the  simple  enunciation  of  this  theory  arise,  as 
a  necessary  consequence,  several  of  those  celebrated 
laws  which  form  the  very  foundation  of  physics. 

It  results  primarily  from  our  hypothesis,  that  the 


Il6       UNITY  OF  NATURAL  PHENOMENA. 

molecules  of  a  gas  may  be  considered  as  every  instant 
moving  in  a  straight  line,  with  a  uniform  velocity 
common  to  the  whole  mass  ;  we  have,  in  fact,  elimi- 
nated the  perturbing  phenomena  existing  at  the  mo- 
ment of  collision.  Is  it  not  henceforth  evident  that,  if 
the  gas  is  confined  in  a  receiver,  the  pressure  exerted 
upon  its  walls  will  be  proportional  to  the  number  of 
atoms  in  the  gas,  that  is  to  say,  to  its  density? 
Equality  of  ratio  between  pressure  and  density,  such, 
we  know,  is  Mariotte's  law. 

Now,  at  the  same  pressure  and  temperature,  differ- 
ent gases  of  the  same  volume  contain  the  same  num- 
ber of  molecules.  This  is  a  fact  which  chemists  par- 
.ticularly  bear  witness  to,  and  it  is  deducible  from  our 
hypothesis.  Since  the  molecular  actions,  properly  so 
called,  may  be  neglected,  it  is  conceivable  that  the 
molecules  of  the  same  gases,  endowed  with  equal 
liberty,  will  arrange  themselves,  other  circumstances 
being  equal,  at  equal  distances  from  each  other,  and  in 
the  same  volume  of  a  gas  the  same  number  will  be 
found.  A  quart  of  hydrogen,  a  quart  of  oxygen,  a 
quart  of  nitrogen,  thus  contain  a  uniform  number  of 
molecules.  What  will  take  place  if  two  gases  are 
mixed  ?  The  same  principle  applies  to  the  mixture, 
no  special  action  resulting  from  the  proximity  of  the 
molecules,  since  the  nature  of  the  molecule  appears  to 


HEAT.  II/ 

have  no  influence  upon  the  phenomenon.  Atmospheric 
air  will  behave  in  this  respect,  like  pure  oxygen  or 
pure  nitrogen..  This  is  the  law  of  gaseous  mixtures 
pointed  out  by  Gay-Lussac. 

Since  the  distance  between  the  molecules  remains 
the  same,  whatever  their  mass,  it  is  to  be  expected 
that  the  same  quantity  of  heat  will  be  necessary  in  all 
the  gases,  to  raise  the  temperature  of  the  elementary 
molecule  one  degree.  It  will  be  objected,  perhaps,  that 
the  heaviest  molecules  will  receive  from  this  quantity 
of  heat  a  less  velocity  ;  this  is  evident ;  but  it  is  also 
evident  that  they  require  a  less  velocity  for  mani- 
festing that  effect  which  we  call  an  elevation  of  one' 
degree  of  temperature.  We  are  then  brought  to  this 
result,  that  the  temperature  of  the  elementary  mole- 
cules of  the  different  gases  is  elevated  one  degree  by 
a  like  quantity  of  heat,  whatever  may  be  their  mass, 
or,  as  chemists  say,  their  atomic  weight.  Under  this 
form  may  be  recognized  a  celebrated  law,  to  which 
Dulong  and  Petit  have  given  their  name. 

Gay-Lussac,  it  is  known,  has  established  that  the 
coefficient  of  expansion  is  uniform  for  all  gases.  Now, 
have  we  not  here  a  natural  result  of  the  facts  we  have 
just  disclosed  ?  These  molecules,  which  are  all  placed 
at  the  same  distance  from  each  other,  and  which  ab- 
sorb the  same  quantity  of  heat  in  order  to  increase 


Il8  UNITY   OF   NATURAL   PHENOMENA. 

their  temperature  one  degree,  ought  they  not  to  sepa- 
rate from  each  other  equally  under  this  increase  of 
temperature  ?  The  experiments  of  Gay-Lussac  have 
shown  that  the  coefficient  of  this  uniform  expansion 
is  2T^  of  the  primitive  volume.* 

This  examination  might  be  continued  ;  but  we  have 
said  enough  to  show  how,  from  our  very  definition 
of  gases,  flow  the  laws  which  characterize  the  gaseous 
state. 

The  laws  of  Mariotte,  Gay-Lussac,  Dulong,  and 
Petit  have  had  a  singular  fate.  Discovered  at  a 
period  when  methods  of  experimenting  were  far  from 
the  perfection  to  which  they  have  since  attained,  they 
were  at  first  regarded  as  absolutely  exact,  and  applica- 
ble, in  full  force,  to  the  different  gases.  When  that 
advance  of  improvement  in  the  methods  of  experi- 
menting, to  which  in  France  is  attached  the  name  of 
M.  Victor  Regnault,  took  place,  these  laws,  till  now  so 
respected,  were  at  fault  in  numerous  cases  ;  they  fell 
into  suspicion  ;  at  least  they  came  to  be  considered  as 
empirical  formulae,  which  represented  in  only  an  ap- 
proximate manner  the  general  course  of  phenomena. 
No  theoretical  conception,  in  fact,  accounted  for  the 

*  Decimally  expressed,  this  coefficient  of  expansion  becomes 
.00367,  according  to  the  Centigrade  scale. 


HEAT.  119 

numerous  perturbations  which  the  exact  methods  em- 
ployed by  scientific  men  gave  evidence  of.  But  now 
we  see  why  gases  obey  but  imperfectly  Mariotte's  law, 
and  those  other  laws  we  have  just  referred  to.  In 
order  to  establish  them,  we  have  been  obliged  to  sup- 
pose that  every  molecule  might  be  considered  as  con- 
stantly endowed  with  a  uniform  and  rectilinear  mo- 
tion, and  we  have  regarded  as  insensible  the  duration 
of  the  periods  in  which  this  motion  was#  interfered 
with.  If  this  duration  becomes  appreciable,  while  at 
the  same  time  remaining  very  slight,  the  arguments 
which  we  gave  cannot  be  repeated  in  their  full  force. 
Here  may  be  seen  the  source  of  much  of  the  distrust 
in  the  old  laws  :  it  may  even  be  seen  how  the  perfect 
gaseous  state  is,  to  a  certain  extent,  but  an  ideal  which 
is  scarcely  realized  in  fact.  Hydrogen  would  seem  to 
attain  to  it  entirely  ;  oxygen  and  nitrogen,  and,  as  a 
consequence,  atmospheric  air,  come  near  to  it ;  but 
carbonic  acid  is  sensibly  removed  from  it.  As  to  va- 
pors, they  behave  like  gases  only  as  they  are  very  far 
from  the  point  of  liquefaction. 

There  are,  then,  but  very  few  perfect  gases  ;  but 
they  furnish  us  with  valuable  information,  in  showing 
us  matter  entirely  disengaged  from  those  attractive 
forces  which  complicate  molecular  phenomena. 

When  we  heat  a  cubic  metre  of  air  under  a  constant 


I2O       UNITY  OF  NATURAL  PHENOMENA. 

pressure,  all  the  living  force  which  the  gas  receives  is 
employed  in  increasing  its  volume  by  ^y-g-  for  every 
degree  of  temperature.*  When,  instead  of  leaving 
the  pressure  constant,  we  prevent  the  gas  from  ex- 
panding, when,  while  heating  it,  we  force  it  to  remain 
enclosed  in  the  space  of  a  cubic  metre,  all  the  living 
force  acquired  by  the  air  is  employed  in  increasing  its 
pressure  ^-yg-  for  every  degree.  If  the  initial  tem- 
perature is  that  of  melting  ice,  f  at  two  hundred  and 
seventy-three  degrees,  the  pressure  of  the  air  is 
doubled. 

The  same  law  holds  true  below  zero.  If,  instead 
of  heating  the  gas,  we  cool  it,  its  pressure  goes  on 
diminishing  -^\-^  for  every  degree.  If  we  could  attain 
to  two  hundred  and  seventy  degrees,  the  gas  would  no 
longer  possess  any  pressure  ;  it  would  be  but  an  inert 
mass  of  molecules,  deprived  of  all  living  force.  This 
is  what  has  been  called  the  absolute  zero  of  tempera- 
ture. There  is  here  a  sort  of  limitation  to  which  it  is 
not  possible  to  attain  in  practice,  and  at  which  all 
molecular  motion  would  cease. 

We  have  been  considering  a  definite  mass  of  air, 

*  That  is,  -j^-g-  for  one  degree  Centigrade ;  this  would  be  the 
same  as  ^¥  for  one  degree  Fahrenheit. 

f  The  temperature  of  melting  ice  is  32°  Fahrenheit,  and  o° 
Centigrade. 


HEAT.  121 

and  we  have  supposed  that  we  were  heating  it  one 
degree,  while  allowing  it  to  expand  in  such  a  manner 
that  the  pressure  should  remain  constant ;  we  have 
afterwards  supposed  that  we  were  heating  it  one  de- 
gree, while  preventing  it  from  changing  its  volume. 
Will  there  be  necessary  in  each  case,  in  order  to 
produce  this  same  elevation  of  temperature,  a  like 
quantity  of  heat  ?  Evidently  not.  Under  a  con- 
stant volume  the  air  has  no  outside  work  to  accom- 
plish. Under  a  constant  pressure  it  must  displace  the 
exterior  obstacle  which  opposes  its  expansion ;  it  has 
thus  a  real  work  to  accomplish.  In  this  second  case 
it  must  absorb  an  excess  of  heat  which  is  exactly  the 
equivalent  of  the  work  done.  The  heat-capacity  un- 
der a  constant  volume,  and  the  heat  capacity  under  a 
constant  pressure,  differ  then  in  a  notable  manner. 
For  air,  they  are  in  the  ratio  of  I  to  1.421.  •  The  dif- 
ference between  these  two  quantities  represents  what 
was  formerly  called  the  latent  heat  of  expansion,  and 
what  is  now  the  precise  equivalent  of  the  work  which, 
the  air  must  do  in  order  to  become  expanded. 

We  may  even  observe  that  it  was  from  this  expan- 
sion of  the  air,  the  numerical  conditions  of  which  have 
for  a  long  time  been  fixed,  that  Dr.  Mayer  sought 
to  obtain,  in  1842,  a  primary  determination  of  the 
mechanical  equivalent  of  heat.  The  number  which 


122       UNITY  OF  NATURAL  PHENOMENA. 

M.  Mayer  deduced  does  not  differ  sensibly  from  that 
which  has  been  definitively  adopted  after  a  series  of 
experiments  of  every  kind. 

We  have  said  that  air  accomplishes  outside  work 
in  expanding ;  such  is  usually  the  case  ;  but  it  may, 
under  particular  circumstances,  expand  without  hav- 
ing performed  any  work.  Now  it  is  the  work  which 
absorbs  the  heat,  and  not  the  expansion  itself;  if  there 
is  no  work  in  the  expansion,  it  is  not  indicated  by  the 
absorption  of  heat. 

This  phenomenon  has,  moreover,  been  proved  by  a 
celebrated  experiment  which  M.  Joule  made  in  1845. 
M.  Joule  took  two  receivers  of  the  same  size,  con- 
nected by  tube  and  stopcock ;  into  one  he  put  air 
under  a  pressure  of  twenty-two  atmospheres,  in  the 
other  he  made  a  vacuum,  and  he  permitted  the  com- 
pressed gas  of  the  first  receiver  to  expand  in  the 
second,  and  a  state  of  equilibrium  soon  ensued  'un- 
der a  uniform  pressure  of  eleven  atmospheres.  In 
order  to  arrive  at  this  state,  the  gas  had  not  had 
any  outside  work  to  do,  and  M.  Joule  showed  that 
the  temperature  was  the  same  at  the  beginning  as 
at  the  end  of  the  experiment.  Doubtless  there  were, 
at  certain  moments,  changes  of  temperature,  but  the 
partial  losses  and  gains  compensated  each  other,  and 
at  the  final  analysis  the  absence  of  work  done  was 


HEAT.  123 

indicated  by  the  absence  of  variation  in  the  tem- 
perature. , 

The  experiment  of  M.  Joule  has  been  repeated 
by  several  scientific  men,  and  in  a  noteworthy  man- 
ner by  M.  Victor  Regnault.  But  it  demands  a  high 
degree  of  precision,  and  is  not  of  a  nature  to  be  re- 
produced in  a  lecture  upon  physics.  Mr.  Tyndall, 
in  his  course  at  the  Royal  Institution,  shows  the 
results  of  it  by  means  of  suitable  and  familiar  ap- 
paratus. 

He  first  takes  a  box  in  which  a  certain  quantity  of 
air  is  compressed,  and  he  opens  its  stop-cock  to  let 
the  gas  escape.  Here  the  gas  no  longer  finds  a 
vacuum  before  it ;  it  must,  in  order  to  expand,  drive 
away  the  external  air ;  it  must  perform  a  work ;  and 
it  is  only  from  itself  that  it  derives  the  necessary 
heat.  There  is,  then,  a  lowering  of  temperature,  and 
Mr..  Tyndall  renders  this  result  visible  by  directing 
the  jet  "upon  the  face  of  a  very  sensitive  thermo-elec- 
tric pile  ;  *  the  needle  of  the  galvanometer  indicates 
the  cooling  of  the  gaseous  jet  Instead  of  the  box  of 
compressed  air,  Mr.  Tyndall  next  takes  an  ordinary 

*  Mr.  Tyndall  has  a  thermo-electric  pile  so  sensitive  that, 
maintained  at  a  temperature  of  about  fifty  or  sixty  degrees,  it 
indicates  at  a  distance  of  twenty  paces  the  heat  which  is  given 
out  by  a  man's  body. 


124  -     UNITY  OF  NATURAL  PHENOMENA. 

pair  of  bellows,  and  in  working  them  he  directs  the 
jet  upon  the  front  of  the  pile.  In  this  case  the  gas 
itself  has  not  to  yield  the  heat  necessary  for  pushing 
away  the  external  air ;  the  hand  of  the  operator  fur- 
nishes the  work  directly ;  it  even  furnishes  it  in  excess ; 
and  the  needle  of  the  galvanometer,  instead  of  indi- 
cating a  diminution,*  marks  an  elevation  of  tempera- 
ture. 

The  theory  of  -heat  is  becoming  more  complete 
every  day ;  but  even  now  it  is  sufficiently  advanced 
to  present  a  respectable  state  of  entirety.  If  it  still 
exhibits  gaps  and  doubtful  points,  the  principal  out- 
lines are  at  least  clearly  marked.  The  molecular 
motions  which  constitute  heat  are  not  immediately 
perceptible  to  our  senses,  but  they  may  be  said  'to 
lack  but  little  of  it.  They  are  even  almost  discerni- 
ble, so  well  known  and  so  exact  are  their  mechani- 
cal effects.  When  the  living  force  passes  from  the 
molecules  to  the  mass  of  a  body,  and  return's  from 
that  mass  to  the  molecules,  thus  appearing  succes- 
sively under  the  form  of  work  and  of  heat,  we  can- 
not observe  these  changes  ;  but  the  phenomena,  a 
little  before  and  shortly  after  the  transformation,  are 
so  well  determined,  that  we  believe  we  see  the- change 
itself. 

Thermo-dynamics   is   a  field  sufficiently  explored  ; 


HEAT.  125 

one  in  which  the  mistakes  of  the  way  are  not  seri- 
ous, and  in  which  one  is  certain,  having  gone  astray, 
to  regain  his  path.  Investigating  electrical  phenome- 
na, we  are  about  to  enter  a  region  far  more  obscure 
and  dangerous. 


126       UNITY  OF  NATURAL  PHENOMENA. 


CHAPTER  IV. 
ELECTRICITY. 

I. 

//  is  necessary  to  determine  the  Electric  Unit,  and  to 
fina(  its  Mechanical  Equivalent. 

WHAT  is  electricity  ?  How  shall  we  regard  that 
common  conception  which  is  based  upon  the  play  of 
a  positive  and  a  negative  fluid  ?  Are  there,  in  reality, 
two  electric  fluids  ?  Is  there  even  one  ? 

We  put  these  questions  ;  but  a  reference  to  the 
premises  already  laid  down  will  leave  but  little  doubt 
as  to  the  kind  of  answers  we  shall  give  them. 

And  first,  the  duality  of  the  fluids  can  no  longer  be 
regarded  other  than  as  a  figurative  expression.  We 
may  even  ask  ourselves  if  it  ever  had  an  appearance 
of  reality.  It  has  all  the  characteristics  of  a  fiction 
of  analysis  ;  it  carries  the  mind  at  once  into  the 
realms  of  mechanics.  In  mechanics,  motions  are 
termed  positive  or  negative,  according  to  their  taking 
place  in  one  direction  or  another  ;  so  the  hypothesis 


ELECTRICITY.  I2/ 

of  a  duality  of  fluids  becomes  resolved  into  a  mathe* 
matical  conception.  , 

Is  there  even  any  special  fluid  to  which  we  must 
attribute  electrical  properties  ?  It  would  doubtless 
seem  proper  to  make  here  at  the  outset,  some  partial 
reply,  and  not  to  decide  this  question  without  some 
reserve ;  but  we  need  not  again  declare  that  we  have 
banished  all  idle  prudence,  and  we  do  not  hesitate  to 
assign,  at  once,  to  the  electric  fluid  a  place  outside  of 
science,  and  send  it  to  join  the  company  of  those  de- 
lusions of  the  past,  —  the  calorific  and  luminous  fluids 
and  the  many  so-called  entities  of  former  times. 

With  regard  to  magnetism,  we  may  leave  it  entirely 
aside,  since  standard  instruction  has  long  ago  traced 
to  one  and  the  same  principle  both  the  magnetic  and 
the  electrical  phenomena;  a  permanent  or  a  tem- 
porary magnet  may  be  regarded  as  the  seat  of  a  series 
of  little  currents  setting  in  the  same  direction. 

The  field  being  now  cleared,  the  question  presents 
itself  to  us  in  this  form  :  Is  electricity  a  motion  of  the 
ether  ?  Is  it  a  motion  of  ponderable  matter  ?  Is  it 
a  motion  of  both  ?  In  a  word,  what  is  the  character 
of  this  motion  ? 

Before  broaching  these  questions,  we  desire  to  call 
attention  to  two  important  and  decisive  points  in  the 
study  of  electricity. 


128       UNITY  OF  NATURAL  PHENOMENA. 

*  Electrical  phenomena  have  been  studied  with  great 
care  during  the  past  few  years  ;  a  vast  number  of  lit- 
tle facts  have  been  collected,  which  present,  however, 
only  a  confused  appearance,  being  badly  grouped,  and 
throwing  but  little  light  upon  each  other.  This  is 
doubtless  due  in  a  measure  to  the  nature  of  the  sub- 
ject ;  but  it  is  also  attributable,  in  part,  to  those  who 
make  the  observations.  One  essential  and  primary 
condition  is  wanting  in  the  researches  which  have 
been  made  here  and  there  on  the  subject  of  electrici- 
ty, namely,  an  agreement  as  to  the  unit  to  which  all 
these  actions  shall  be  referred. 

We  have  already  had  occasion  to  mention  the  capi- 
tal importance  that  attaches,  in  physics,  to  the  choice 
of  units.  Every  phenomenon  results  from  the  coex- 
istence of  a  certain  number  of  correlated  facts,  and  in 
order  to  illustrate  the  relation  of  these  facts,  it  is 
necessary  to  represent  each  of  them  in  its  proper 
quantity  by  a  particular  variable.  Thus,  if  we  try  to 
define  the  orbit  of  a  planet  about  the  sun,  we  must 
take  for  the  elements  of  our  research,  on  the  one  hand, 
the  variable  length  of  the  radius  vector  which  joins  the 
sun  to  the  planet,  and  on  the  other,  the  constantly 
changing  inclination  of  this  radius  to  the  axis  of  the 
perihelion  ;  observation  will  show  forthwith  the  rela- 
tion between  these  two  quantities  which  constitutes  the 


ELECTRICITY.  I2Q 

equation  of  the  ellipse,  and  we  may  declare  that  the 
planet  runs  in  an  elliptical  orbit*  in  which  the  sun  oc- 
cupies one  of  the  foci.  It  would  not  do,  however,  to 
suppose  that  a  phenomenon  -would  be  equally  easy  to 
define  with  any  variables  whatever  that  might  be  se- 
lected ;  on  the  contrary,  this  selection  exerts  a  very 
decisive  influence  upon  the  results  obtained.  With 
certain  variables  you  will  arrive  at  only  confused  re- 
sults, from  which  you  can  derive  no  profit,  while  with 
others,  we  shall  bring  to  light  precise  laws. 

We  might  thus  mention,  in  the  history  of  physical 
science,  many  an  unfortunate  selection  which  has  re- 
tarded important  discoveries,  likewise  also  many  for- 
tunate guesses.  An  example  of  the  latter  occurred 
in  the  case  of  Kepler's  first  law,  the  second  of  which 
we  just  now  alluded  to.  When  Kepler  sought  the  law 
of  the  motion  of  a  planet  in  its  orbit,  he  selected  as 
variables  the  time,  and  the  areas  described  by  the 
radius  vector.  It  would  have  been  just  as  natural, 
more  so  perhaps,  to  seek  a  relation  between  the  time 
and  one  of  the  variables  mentioned  above,  namely,  the 
length  of  the  radius,  or  its  inclination  to  the  line  of 
the  apsides.  Had  Kepler  pursued  this  course,  he 
would  not  have  found  any  simple  relation  between  the 
numerical  values  resulting  from  his  observations  and 
those  of  Tycho-Brahe ;  the  intimate  connection  of 


I3O       UNITY  OF  NATURAL  PHENOMENA. 

these  values  would  have  been  concealed  under  rela- 
tions so  complicated  that  it  never  could  have  been 
demonstrated.  On  the  contrary,  thanks  to  the  varia- 
bles he  had  chosen,  Kepler  was  readily  able  to  ob- 
serve that  the  numerical  values  representing  the  times, 
and  those  representing  the  areas,  formed  two  propor- 
tional series.  In  this  way  became  plainly  evident  that 
great  law  of  astronomy,  which  we  express  by  saying 
that  the  areas  described  by  the  planets  are  in  pro- 
portion to  the  times,  or  that  planets  describe  equal 
areas  in  equal  times. 

A  fortunate  selection  of  variables  is,  then,  indeed 
an  essential  condition  of  success,  and  constitutes  al- 
most the  chief  difficulty  in  all  physical  researches. 
How  much  more  important  becomes  this  considera- 
tion when  we  are  treating,  not  of  quantities  which 
serve  to  verify  a  particular  law,  but  of  those  which 
form  the  standard  of  a  whole  class  of  phenomena. 

We  now  see  the  first  step  to  be  taken  by  electri- 
cians. They  must  agree  upon  some  common  and  con- 
venient measure  of  electrical  actions.  Failing  in  this 
agreement,  they  work  each  for  himself,  unable  to  .sys- 
tematize their  discoveries,  and  never  arriving  at  a 
mutual  understanding  ;  there  reigns  among  them  a 
confusion  of  tongues. 


ELECTRICITY.  131 

Who  will  put  an  end  to  this  ?  Who  will  furnish  a 
basis  of  common  agreement  ?  ' 

Five  years  ago  the  British  Association  made  lauda- 
ble efforts  in  this  direction.  The  British  Association 
is,  as  is  well  known,  a  private  society,  devoting  itself, 
in  England,  to  the  advancement  of  science,  and  whose 
watchful  attention  is  directed  successively  to  all  points 
where  there  is  urgent  need  of  making  investigations. 
To  aid  the  progress  of  the  submarine  telegraph,  it  ap- 
pointed, in  1862,  a  commission,  which  examined  the 
whole  question  of  the  measure  of  electrical  phenom- 
ena, and  proposed  a  solution  strictly  applicable,  though 
very  complicated.* 

*  A  previous  commission  had  been  instituted  in  1861.  Its  spe- 
cial object  was  to  determine  a  scale  of  resistance  by  which  to  test 
the  value  of  submarine  cables,  manufactifred  in  English  work- 
shops, .with  respect  to  their  transmitting  qualities.  The  labors 
of  the  British  Association  have  exerted  no  small  influence  on  the 
wonderful  improvements  whiph  have  been  brought  about  in  the 
manufacture  of  cables  in  England,  which  have  at  last  resulted  in 
establishing  between  Europe  and  America  telegraphic  communi- 
cation. The  commission  of  1861  was  succeeded,  in  1862,  by  a 
new  commission,  consisting  of  Messrs.  Wheatstone,  Thompson, 
C.  W.  Siemens,  and  Charles  Bright.  This  new  commission  has 
not  limited  its  work  to  the  measurement  of  resistances ;  it  has 
confronted  the  whole  question  of  electric  units,  seekingto  connect 
them  closely  with  the  units  employed  in  mechanics.  Experi- 
ments have  been  made  at  King's  College  to  determine  what  de- 
gree of  precision  is  practically  attainable  through  the  application 


132       UNITY  OF  NATyRAL  PHENOMENA. 

In  France  this  problem  would  not  even  seem  to  be 
the  order  of  the  day.  We  have,  it  is  true,  an  associa- 
tion for  the  advancement  of  the  physical  science  of 
the  globe ;  but  its  members  would  seem  to  have 
nothing  left  to  desire,  while  they  have  the  moon 
pointed  out  to  them  every  month  at  the  obser- 
vatory. 

Meanwhile,  be  the  question  of  electric  units  de- 
cided on  this  side  of  the  channel  or  the  other,  the 
study  of  heat  clearly  indicates  the  character  of  the 
solution  which  must  eventually  result.  So  long  as 
calorific  effects  were  estimated  merely  by  changes  in 
the  thermometer,  we  remained  on  the  outside  of  phe- 
nomena, and  knew  nothing  of  their  essential  nature. 
Temperature  is  only  one  of  the  rTeculiarities  of  heat. 
I  have  a  kilogramrne  of  water  at  one  hundred  degrees 
Centigrade.  If  it  evaporates  freely  in  the  air,  it  ab- 
sorbs the  enormous  quantity  of  536  heat  units,  and 
the  kilogramme  of  vapor  which  results  is  still  at  one 
hundred  degrees.* 

of  the  theoretical  views  of  the  commission.  The  result  of  these 
investigations  is  contained  in  a  report  drawn  up  by  Mr.  Fleeming 
Jenken,  and  published  by  the  commission  in  the  form  of  an  ap- 
peal to  the  scientific  world. 

*  Sometimes  a  very  elegant  experiment  is  made  in  the  labora- 
tory, showing  that  different  bodies,  while  at  the  same  tempera- 
ture, contain  very  different  quantities  of  heat.  A  cake  of  bees- 


ELECTRICITY.  133 

Between  the  motions  which  take  place  in  the  inte- 
rior of  bodies  and  the  variations  they  effect  upon  the 
thermometric  scale,  there  exist  only  indirect,  and,  so 
to  speak,  accidental  relations.  The  study  of  these  re- 
lations has  never  afforded  more  than  vague  and  con- 
fused information.  Real  progress  began  the  day  when 
calorific  phenomena  were  no  longer  referred  to  the  de- 
grees of  the  thermometer  only,  but  to  an  intrinsic  unit, 
—the  heat  unit ;  that  is  to  say,  the  entire  quantity  of 
heat  necessary  to  effect  a  certain  definite  result,  and 
one  easy  to  appreciate. 

Hitherto*  the  galvanometer  has  been  almost  exclu- 
sively employed  as  the  measure  of  electrical  phe- 
nomena. Now,  we  may  remark  in  passing,  that  the 
galvanometer  is  a  far  more  imperfect  instrument  than 


wax,  about  twelve  millimetres  in  thickness,  is  suspended  from  a 
support;  next  a  vessel  of  boiling  oil  is  taken,  and  balls  of  differ- 
ent metals  of  the  same  size  are  plunged  into  it —  balls  of  iron, 
copper,  tin,  lead,  and  bismuth,  for  example.  These  balls,  hav- 
ing all  taken  the  same  temperature,  that  of  the  boiling  liquid, 
are  taken  out  of  the  oil,  and  placed  all  at  once  upon  the  cake  of 
wax.  They  sink  into  the  wax,  but  with  different  degrees  of 
rapidity.  The  iron  and  the  copper  enter  powerfully  into  the 
melting  mass;  the  tin  more  gently;  the  lead  and  bismuth  re- 
main behind.  The  iron  ball  passes  through  the  wax,  and  falls 
out  first;  the  copper  one  follows  it;  the  others  remain  in  it,  un- 
able to  pierce  the  cake,  and  stop  there  at  different  depths,  ac- 
cording to  the  laws  of  their  calorific  capacity. 


134       UNITY  OF  NATURAL  PHENOMENA. 

the  thermometer  even.  The  thermometer,  at  least, 
indicates  directly  by  its  linear  expansions  that  part  of 
the  calorific  matter  it  is  required  to  exhibit.  The  gal- 
vanometer, which  also  indicates  but  a  part  only  of  the 
electrical  effect,  has  the  further  disadvantage  of  exhib- 
iting them  only  by  the  angular  variation  of  a  needle. 
We  are,  then,  obliged  to  compare  angles,  that  is,  to 
estimate  sines  and  tangents.  Already  excluded  from 
actual  contact  with  the  facts,  the  observer  finds  them 
still  further  masked  by  trigonometrical  functions. 

There  is,  then,  urgent  need  of  penetrating  to  the 
very  core  of  phenomena.  In  all  our  succeeding  inves- 
tigations, we  must  take  for  our  fundamental  idea  the 
electric  unit,  that  is,  the  amount  of  electricity  required 
to  produce  a  fixed  result. 

What  shall  be  the  effect  henceforward  selected  for 
our  type  ?  Here  is  a  question  admitting  of  discussion. 
Suppose,  just  to  fix  our  ideas,  we  select  the  voltaic 
decomposition  of  a  kilogramme  of  water.  The  electric 
unit  thus  determined,  we  shall  be  compelled  to  express, 
by  means  of  this  fundamental  unit,  the  various  electri- 
cal phenomena  that  have  hitherto  been  characterized 
only  by  special  circumstances,  by  the  intensity  of  the 
current,  or  by  the  amount  of  heat  developed.  Instead 
of  halting  at  partial  effects,  we  shall  approach  the  facts 
as  a  whole.  Out  of  the  mass  of  incoherent  observa- 


ELECTRICITY.  135 

tions  now  presented  by  the  science  of  electricity  there 
will  arise  a  sort  of  natural  selection  ;  isolated  laws  will 
be  gathered  into  groups,  and  their  inner  meaning 
made  manifest. 

To  choose  the  electric  unit, — this  is  the  first  step  in 
advance  to  be  made  by  electricians  ;  the  second  is  to 
ascertain  the  mechanical  equivalent  of  electricity ;  to 
find  out  how  many  kilogrammetres  are  equivalent  to 
an  electric  unit. 

We  now  see,  by  a  characteristic  example,  the  utility 
of  a  hypothesis  capable  of  comprehending  natural 
phenomena  as  a  whole,  and  of  tracing  them  back  to  a 
single  principle.  By  it  the  natural  philosopher  may 
be  guided  in  the  imperfectly  known  regions  he  ex- 
plores ;  by  it  instructed  in  the  path  he  must  pursue 
through  the  labyrinths  of  particular  facts. 

Let  us  observe,  however,  that  in  order  to  take  the 
two  steps  we  have  mentioned,  it  is  not  necessary  to 
get  a  preliminary  view  of  the  nature  itself  of  elec- 
tricity. If  we  look  into  the  history  of  heat,  we  shall 
see  that  the  notion  of  a  heat  unit  was  not  at  all  pecu- 
liar to  those  who  regarded  heat  as  a  motion.  It  might 
even  be  remarked  that  this  unity  has  a  suspicious 
look,  and  that  it  savors  a  little  of  the  doctrine  of  the 
materiality  of  caloric.  The  equivalence  of  heat  and 
mechanical  work  has  also  been  established  outside 


136       UNITY  OF  NATURAL  PHENOMENA. 

of  all  theory.  This  notion  of  equivalence  is  a  pru- 
dent and  eclectic  one ;  it  involves  no  preconceived  idea 
as  to  the  facts  one  is  comparing  ;  they  are  equivalent, 
nothing  more.  When  one  is  sure  that  he  is  com- 
paring together  two  motions,  the  words  equivalent 
and  equivalence  become,  so  to  speak,  inadequate,  and 
he  has  the  right  to  resort  to  more  energetic  terms. 

First,  to  decide  upon  the  electric  unit,  and  then  to 
determine  its  mechanical  equivalent,  such  are  the  two 
points  to  which  the  efforts  of  electricians  must  first  be 
directed,  and  the  ones  we  have  desired  to  bring  to  view. 
Having  given  these  general  suggestions,  it  remains  for 
us  to  show  what  experience  teaches  us  at  present 
with  regard  to  the  conditions  which  characterize  the 
electric  motion. 


II. 


The  Electric  Current  apparently  a  Transport  of  Ethereal 
Matter. 

THE  preliminaries  just  laid  down  show  clearly 
enough  that  we  are  far  from  possessing  a  general 
theory  in  regard  to  electrical  phenomena. 

We  were  not  in  want  of  experimental  data.  Ob- 
servers have  placed  at  our  disposal  a  large  numbe/  of 
facts,  too  many,  almost,  since  the  special  laws  estab- 


•  ELECTRICITY.  137 

lished  by  them  are  not  referable  to  a  few  principal 
groups  ;  they  exhibit  only  orie  phase  of  each  phe- 
nomenon, and  have,  for  the  most  part,  but  an  obscure 
and  commonplace  significance.  Nevertheless,  from  a 
general  view  of  these  confused  observations,  we  con- 
clude that  electric  motion  is  a  real  transfer  of  mat- 
ter ;  the  word  current,  employed  in  ordinary  language, 
would  thus  correspond  to  the  real  nature  of  the  phe- 
nomena. 

A  decisive  consideration  may  be  brought  to  the 
support  of  this  opinion.  If  the  two  poles  of  a  bat-* 
tery  are  connected  by  a  conductor  of  variable  dimen- 
sions, the  intensity  of  the  current,  as  measured  by 
its  effects  on  the  galvanometer,  is  the  same  in  every 
part  of  this  conductor  ;  wherever  it  becomes  thinner, 
there  the  current  is  more  rapid,  so  that  each  segment 
gives  passage  in  the  same  period  of  time  to  the  same 
amount  of  electricity.  This  peculiarity  is  easily  made 
visible  by  its  calorific  or  luminous  effects.  We  know 
that  if  a  very  fine  wire  is  interposed  in  the  passage  of 
a  current  it  grows  red,  and  becomes  heated  even  so 
far  as  to  melt.  We  are  also  acquainted  with  the  ex- 
periments made  with  Geissler's  tubes.  These  are 
glass  tubes,  in  which  the  air  is  rarefied,  and  which  are 
laid  in  the  course  of  the  current,  in  order  that  the  elec- 
tricity may  traverse  them  in  the  form  of  a  luminous 


138       UNITY  OF  NATURAL  PHENOMENA. 

spray.  Now,  if  we  take  a  Geissler's  tube,  varying  in 
size  in  its  several  sections,  we  may  easily  demonstrate 
that  the  spray  becomes  the  more  luminous  the  nar- 
rower the  tube.  In  the  fact  that  the  motion  increases 
in  proportion  as  the  calibre  of  the  tube  diminishes, 
we  recognize  a  fundamental  law  of  the  flow  of  liquids  ; 
a  law  known  since  the  time  of  Leonardo  di  Vinci. 
This  fact  alone  excludes  the  idea  that  electricity  may 
be  the  result  of  simple  vibrations.  It  does  not  ap- 
pear, in  fact,  in  any  of  the  vibratory  motions  we 
*are  acquainted  with,  whether  longitudinal,  like  those 
of  sound,  or  transversal,  like  those  of  light. 

When  these  latter  motions  encounter  an  obstacle 
which  contracts  the  medium  in  which  they  are  dis- 
played, they  are  reflected  into  the  body  of  the  medium ; 
but  they  do  not  hurry  forward  into  the  open  space 
before  them  ;  it  is  those  fluids  which  are  endowed 
with  a  motion  of  transportation  that  are  thus  accel- 
erated in  narrow  passages.  When  an  iron  rod  is 
heated,  we  do  not  observe  the  temperature  to  be  any 
higher  in  those  parts  where  the  rod  is  thin.  The  case 
is  otherwise  when  the  elevation  of  temperature  is 
caused  by  electricity,  since,  as  was  just  now  stated, 
very  fine  wires  placed  in  the  circuit  of  an  ordinary 
conductor  may  be  heated  to  a  red  heat  and  melted  . 

We  find,  then,  at  the  outset,  by  means  of  a  funda- 


ELECTRICITY.  139 

mental  fact,  that  the  .electric  motion  is  similar  to  the 
flowing  of  a  fluid.  This  analogy  may  be  traced 
through  all  the  particulars  revealed  by  experiment. 

The  science  of  telegraphy,  especially,  has  furnished 
us  numerous  hints  in  this  direction.  A  telegraphic 
wire  is  like  a  tube  which  is  to  be  filled  ;  the  bat- 
tery is  like  a  reservoir  which  fills  the  tube  more  or 
less  easily,  according  to  the  degree  in  which  it  is 
itself  filled.  Be  the  wire  charged,  or  half  charged, 
when  the  end  which  communicates  with  the  battery 
is  placed  in  the  ground,  a  part  of  the  charge  flows 
back.  The  case  is  similar  with  a  liquid  flowing  from 
a  tube  open  at  both  ends.  Nothing  of  the  kind  would 
have  taken  place  in  the  case  of  a  vibratory  motion  ; 
such  a  motion,  when  the  cause  producing  it  has  ceased, 
does  not  take  a  backward  direction,  but  continues 
precisely  in  that  in  which  it  began. 

By  such  examples  we  are  guided  in  considering  the 
duration  of  the  propagation  of  a  current,  that  is,  the 
time  necessary  for  the  current  to  attain  a  uniform 
state  throughout  the  whole  extent  of  the  wire  ;  and 
here  again  we  are  reminded  of  the  transport  of  a*fluid, 
since  the  time  increases  nearly  in  proportion  to  the 
square  of  the  length  of  the  wire.  This  time  varies  in- 
versely as  the  diameter  of  the  wire,  and  this  fact  alone 
shows  'that  we  have  not  to  do  with  a  vibration  ;  a  vi- 


I4O       UNITY  OF  NATURAL  PHENOMENA. 

bratory  motion,  in  fact,  assumes  its  uniform  condition 
as  rapidly  in  a  large  tube  as  in  a  small  one.  This  may 
be  verified  in  the  case  of  sound. 

But  what  is  this  fluid,  the  transportation  of  which 
constitutes  the  electric  current  ?  Is  it,  perchance, 
ponderable  matter  itself,  reduced  to  a  state  of  vapor, 
or  at  least  brought  to  a  condition  of  tenuity,  which 
imparts  to  it  the  properties  of  fluids  ?  Certainly  not. 
For,  in  the  first  place,  we  have  no  reason  to  suppose 
that  the  passage  of  a  fluid  through  a  wire  augments 
its  weight ;  besides,  if  the  electric  flux  were  a  trans- 
port of  ponderable  matter,  if  the  matter  itself  of  the 
conductors  were  transported,  it  ought  to  be  perceptible 
when  two  unlike  wires  are  joined  to  each  other ;  when 
the  current,  after  passing  through  a  copper  wire,  for 
example,  passes  into  an  iron  one,  the  copper  ought  to 
leave  some  traces  of  its  passage  through  masses  of  the 
iron,  and  vice  versa.  Observation  has  not  disclosed 
any  fact  of  the  kind,  unless  it  be  at  the  very  point  of 
junction.  Even  here,  we  must  admit,  the  transporta- 
tion of  matter  is  a  mere  accident,  an  accessory  phe- 
nemegon,  a  purely  local  circumstance,  that  may  be  neg- . 
lected  without  hesitation. 

Are  not  our  conclusions,  then,  self-established  ? 
This  fluid,  which  is  carried  along  a  conductor,  is 
nothing  else  than  the  imponderable  matter  we  are 


ELECTRICITY.  14! 

acquainted  with  under  the  name  of  ether.  The  elec- 
tric motion  of  the  ether  is,  moreover,  in  no  sense  a  vi- 
bratory one  ;  it  is  a  veritable  flux,  an  actual  transport. 

We  cannot  but  be  confirmed  in  these  opinions  if  we 
make  a  further  hasty  examination  of  some  of  the  pecu- 
liarities presented  by  these  currents. 

The  electric  spark  has  been  thoroughly  investigated. 
It  offers  an  interesting  subject  for  study.  Physicists 
have  always  hoped  to  find  here,  under  a  striking  form, 
some  direct  information  concerning  the  nature  of  elec- 
tricity. They  have  especially  studied  the  spark  pro- 
ceeding from  static  machines  ;  but  their  conclusions 
might  legitimately  be  extended  to  that  produced  by 
currents. 

It  is  necessary  to  state  that  the  study  of  the  spark 
has  long  been  productive  of  deceptive  arguments,  and 
especially  has  it  been  of  service  to  the  theory  of  two 
fluids.  On  beholding  the  spark,  compact  and  brilliant 
at  both  poles,  but  larger  and  dimmer  at  its  centre,  one 
was  sure  that  he  saw  the  two  different  fluids  in  the 
very  act  of  combination.  There  was  the  positive  fluid 
proceeding  from  one  pole  in  the  form  of  a  fan,  and  the 
negative  fluid  escaping  from  the  other  in  the  form  of  a 
star.  To  us  the  brilliancy  of  the  two  poles  seemed  to 
proceed  from  the  agitation  produced  in  them  by  the 
electric  flow  ;  but  the  flow  may  likewise  produce  this 


142        UNITY  OF  NATURAL  PHENOMENA. 

effect  when  escaping  from  one  side  and  entering  the 
other. 

Nevertheless,  to  prove  that  a  fluid  passed  out  of 
both  sides  at  the  same  time,  an  experiment  was  made, 
which  f  seemed  decisive.  The  spark  was  made  to 
pierce  several  sheets  of  paper,  and  it  was  shown  that 
the  edges  of  the  aperture  were  turned,  some  towards 
the  negative  pole,  some  towards  the  positive  pole,  — 
a  fallacious  result,  and  one  from  which  no  conclusion 
can  be  drawn  as  to  the  direction  of  the  electric  cur- 
rent at  either  pole.  In  many  cases  a  body  forcibly 
punctured  exhibits  edges  turned  in  a  contrary  direc- 
tion to  that  of  the  pressure.  It  would  look,  therefore, 
as  if  the  penetrating  body  has,  in  the  second  stage  of 
the  perforation,  experienced  a  rebound.  The  symme- 
try of  the  ridge  raised  on  both  faces  of  the  sheets 
pierced  by  the  spark  affords,  therefore,  no  proof  of  the 
passage  of  a  double  fluid. 

On  the  contrary,  the  recent  advancements  in  spec- 
troscopy  go  to  prove  the  unity  of  the  motion.  It  has 
been  proved  that  the  spectrum  of  the  spark  depends 
upon  the  nature  of  the  metal  composing  the  positive 
pole,  since  it  remains  unchanged  when  the  nature  of 
the  other  pole  is  altered  ;  the  metallic  particles  carried 
along  by  the  current  show,  then,  that  the  transfer 
takes  place  in  a  single  direction. 


ELECTRICITY.  143    . 

Another  important  fact  is,  that  the  spark  is  strati- 
fied. It  is  seen  in  layers  ranged  one  upon  the  other. 
It  would  appear,  in  fact,  as  if  the  electric  flow  was  not 
a  continuous  one.  We  have  here  developed  a  phe- 
nomenon similar  to  that  which  is  produced  when  we 
see  smoke  issuing  from  a  chimney  in  successive  puffs. 
When  a  flowing  body,  meets  an  obstacle,  it  produces, 
in  the  effort  to  overcome  that  obstacle,  certain  onward 
movements  which  arrange  themselves  over  each  other. 
May  not  also  the  stratification  of  the  electric  spark  be 
like  the  transfer  of  metallic  particles  —  a  purely  local 
accident  ?  May  it  not  indicate  a  state  of  things  exist- 
ing throughout  the  whole  extent  of  'the  conductor  ? 
We  might  assert,  then,  that  the  transportation  of  the 
ether  is  effected  by  successive  waves  ;  but  these  waves, 
which  accompany  a  movement  of  transportation,  must 
not  at  all  be  confounded  with  vibratory  waves,  of 
which  light  and  sound  are  examples. 

It  will  be  seen  that  we  make  here  an  important 
reservation.  We  have  thus  far  admitted  that  the 
ether  is. really  carried  from  one  end  to  the  other  of 
the  conductor  ;  that  each  atom  employed  in  the  circuit 
runs  through  its  entire  length.  It  is  possible,  on  the 
other  hand,  that  each  atom  is  permitted  only  a  partial 
range,  and  that  the  current  is  produced  somehow  by  a 

* 

series  of  relays  more  or  less  near  together.     We  leave 


144        UNITY  OF  NATURAL  PHENOMENA. 

the  door  wide  open  for  such  a  supposition,  which  is  in 
no  way  incompatible  with  what  we  have  above  stated  ; 
but,  for  simplicity's  sake,  we  shall  continue  to  speak  as 
if  we  were  treating  of  a  fluid  in  motion,  the  particles 
of  which  all  pass  through  the  entire  circuit. 

One  other  question  presents  itself  in  the  study  of 
the  spark,  — -  a  question  of  high  importance,  and  one 
which  can  be  only  partially  answered.  Is  the  spark 
produced  in  a  perfect  vacuum  ?  In  other  words,  can 
the  electric  stream,  even  though  it  be  itself  nothing 
but  a  motion  of  ether,  exist  outside  of  ponderable 
matter  ?  The  importance  of  this  question  is  manifest, 
and  it  finds  no  answer  in  the  general  phenomena  of 
nature.  The  sun  sends  us  light ;  we  receive  electricity 
from  it,  not  directly  but  mediately.  The  frequent  ex- 
periments made  to  discover  whether  the  electric  spark 
can  pass  through  an  absolute  void,  have  been  subject 
to  much  dispute.  How  shall  we  procure  an  absolute 
void  ?  We  try  to  empty  a  tube  of  all  ponderable  mat- 
ter ;  we  fill  it  several  times  with  carbonic  acid,  which 
we  expel  by  means  of  an  air-pump,  and  finally  we  use 
potash  to  absorb  the  remains  of  the  acid  ;  but  are 
there  not  vapors  escaping  from  the  joints,  from  the 
valves  of  the  machine,  and  from  the  potash  itself? 
How  get  rid  of  this  source  of  error  ?  Therefore,  we 
'repeat,  nothing  could  be  less  satisfactory  than  the 


ELECTRICITY.  145 

result  of  such  an  experiment.  The  attempts  which 
have  been  made,  however,  go  to  prove  that  the  spark 
does  not  pass  through  a  vacuum,  and  from  considera- 
tions of  quite  another  kind  we  are  led  to  the  same 
conclusion.  It  would  seem,  then,  that  the  electric 
movement  can  only  be  produced  in  the  midst  of  pon- 
derable matter.* 

Let  us  now  direct  our  attention  to  those  phenomena 
in  which  currents  have  their  rise,  the  two  principal 
ones  being  heat  and  chemical  action.  How  shall  we 
conceive,  in  either  case,  of  the  beginning  of  a  current  ? 
If  two  metallic  bars,  one  of  bismuth  and  one  of  anti- 
mony, for  instance,  are  soldered  at  one  end,  and  we 
heat  the  point  of  union,  a  current  arises  in  the  arc 
connecting  the  two  metals.  Such  is  the  principle  of 
the  thermo-electric  pile.  Observe  that  we  must  have, 
at  the  place  where  the  heat  is  applied,  different  metals  ; 
a  junction  of  different  sections  of  the  same  conductor 
would  not  suffice  to  produce  a  current ;  we  must  have 


*  This  statement  seems  to  be  confirmed  by  experiments  made 
with  PlOcher's  tubes,  used  in  spectrum  analysis.  In  a  tube,  re- 
duced as  nearly  as  possible  to  a  vacuum,  no  spark  is  observed, 
although  the  platinum  wires  on  the  ends  of  the  tube  are  very 
closely  approximated.  In  a  second  tube,  containing  the  slightest 
possible  quantity  of  hydrogen,  the  light  of  the  passing  spark  is 
clearly  visible.  (See  Schellen's  Spectrum  Analysis,  p.  26.)  — 
Translator. 

10 


146       UNITY  OF  NATURAL  PHENOMENA. 

molecules  which  are  unlike  ;  and  what  does  this  sig- 
nify ?  Let  us  refer  again  to  the  hypothesis  we  have 
constructed  to  explain  how  bodies  pass  from  a  gaseous 
to  a  liquid  and  solid  state.  We  were  compelled  to  ad- 
mit that  every  molecule  carries  along  with  it  in  its 
rotation  a  sort  of  atmosphere  of  ether.  When  unlike 
molecules  are  placed  side  by  side,  then  there  will  be  a 
meeting  of  atmospheres  of  different,  densities  and  ve- 
locities ;  and  if  their  equilibrium  becomes  disturbed  by 
the  application  of  heat,  we  may  see  how  this  circum- 
stance would  set  free  a  certain  number  of  ethereal 
atoms.  These  atoms  rush  into  the  conductor  as  into 
a  channel,  and  there  form  the  current.  The  more  dis- 
cordant are  the  atmospheres  of  the  two  metallic  ele- 
ments, the  more  intense  will  be  the  effect ;  there  will 
be  no  effect  when  the  atmospheres  are  all  alike,  that 
is,  when  only  one  metal  is  employed.  Chemical  action 
produces  an  analogous  effect  on  a  larger  scale.  When 
two  bodies  combine,  the  molecular  atmospheres  are 
powerfully  disturbed ;  a  new  distribution  of  the  ether 
is  forcibly  effected  about  the  new  molecules,  and  this 
sudden  change  drives  away  more  or  less  of  the  ethereal 
atoms.  Thus  different  batteries,  the  thermo-electric 

pile  as  well  as  those  based  on  a  chemical  combination, 

% 

exhibit  at  the  very  origin  of  the  current  the  beginning 
of  a  flow  of  ether. 


ELECTRICITY.  147 

Beginning  in  the  pile,  this  flow  is  continued  in  the 
conductor,  and  if  we  regard  'the  entire  circuit  thus 
formed,  we  shall  readily  see  that  chemical  action, 
electricity,  heat,  mechanical  work,  are  all  produced 
according  to  that  law  of  mutual  transformation  to 
which  we  are  compelled  to  reduce  all  physical  phe- 
nomena. 

The  vis  viva  due  to  the  action  of  the  pile  sets  the 
ether  in  motion  ;  this,  circulating  in  the  conductor, 
develops  in  it  heat,  because  it  agitates  in  its  passage 
the  ponderable  molecules,  and  leaves  them  a  part  of 
its  vis  viva.  But  instead  of  producing  heat,  it  may 
produce  work  of  a  different  kind. 

We  shall  find  a  ready  example  of  this  by  placing  in 
the  circuit  a  voltameter,*  filled  with  water.  The  two 
poles  of  the  current,  the  two  electrodes  of  platinum 
being  directed  into  the  upper  part  of  the  liquid,  the 
water  becomes  warm,  and  soon  boils ;  then  if  the  poles 
be  more  deeply  plunged  into  the  vessel,  the  water  be- 
gins to  resolve  itself  into  its  two  elements,  the  tem- 
perature of  the  liquid  diminishes,  and  we  observe  very 
soon  the  ordinary  conditions  of  electrolytic  decomposi- 

*  An  instrument  to  measure  the  strength  of  an  electric  current, 
consisting  of  a  graduated  tube,  which  receives  and  measures  the 
amount  of  gas  generated  by  the  current  in  a  given  time.  — 
Translator. 


148       UNITY  OF  NATURAL  PHENOMENA. 

tion  which  are  accompanied  by  a  slight  elevation  of 
temperature. 

We  see  here  an  electrolytic  and  a  calorific  action 
directly  exchanging  with  each  other.  If  the  experi- 
ment was  so  conducted  as  to  yield  precise  measure- 
ments, if  we  were  able  to  free  it  from  every  source  of 
error,  we  should  discover  just  what  weight  of  water 
may  be  heated  one  degree  by  the  quantity  of  elec- 
tricity which  will  decompose  a  given  weight  of  that 
water  ;  in  other  words,  we  should  find  the  relation  be- 
tween the  electric  unit  and  the  heat  unit,  and  electric 
currents  would  thus  be  reduced  to  the  common  meas- 
ure of  mechanical  work,  to  the  kilogrammetre.* 

In  the  example  we  have  given,  the  current  produces 
a  chemical  work ;  it  might  also  produce  a  mechanical 

*  Father  Secchi  has  made  some  experiments;  from  which  we 
might  conclude  that  the  quantity  of  electricity  which  decomposes 
0.106  gramme  of  water,  would  raise,  by  one  degree,  the  tem- 
perature of  thirty-eight  grammes  of  the  same  liquid.  Taking  for 
our  electric  unit,  as  we  have  above  suggested,  the  quantity  of 
electricity  capable  of  decomposing  a  kilogramme  of  water,  it  will 
be  found  that  .an  electric  unit  is  equal  to  three  hundred  and  sixty 
heat  units,  or  one  hundred  and  fifty-three  thousand  kilogramme- 
tres.  If,  for  the  sake  of  smaller  numbers,  we  compare  the  elec- 
tric unit  with  the  gramme,  it  will  then  be  equivalent  to  0.36  heat 
units,  or  one -hundred  and  fifty-three  kilogrammetres.  We  give 
this  result,  but  we  are  not  willing  to  certify  that  the  experiment 
from  which  it  is  derived  can  be  regarded  as  covering  all  the  con- 
ditions of  the  problem. 


ELECTRICITY.  149 

work,  —  raise  a  weight,  or  1,urn  a  shaft,  M.  Favre,  in 
his  series  of  well-known  experiments,  has  shown  that 
the  heat  developed  in  a  current  decreases  precisely  in 
proportion  to  the  work  produced.  The  vis  viva  of  the 
electric  current  is  in  part  consumed  by  the  lifting  of 
the  weight  or  the  turning  of  the  shaft,  and  the  calorific 
disturbance  of  the  circuit  is  diminished  in  proportion. 
We  see  electricity  converted  into  work,  instead  of  being 
transformed  into  heat ;  if  this  conversion  could  be  com- 
plete, if  we  were  able  to  eliminate  entirely  from  the 
experiment  the  manifestation  of  heat,  we  might  at 
length  determine  exactly  the  ratio  of  equivalence  be- 
tween electricity  and  mechanical  work  ;  we  might  ob- 
serve directly  the  relation  between  the  electric  unit 
and  the  kilogram  metre. 

•  But  this  is  a  purely  theoretical  conception  ;  if,  as  is 
probable,  the  electric  flow  takes  place  only  through 
ponderable  matter,  it  necessarily  sets  in  motion  its 
molecules  ;  that  is  to  say,  there  is  no  electricity  with- 
out heat.  We  must  mention  in  this  connection,  that 
the  conductibility  of  different  substances  follows  al- 
most the  same  order,  both  for  electricity  and  for  heat. 
If,  for  example,  we  regard  the  metals  in  this  twofold 
relation,  not  only  do  they  arrange  themselves  in  both 
cases  in  the  same  order  (silver,  copper,  gold,  tin,  iron, 
lead,  platinum,  bismuth),  but  the  same  series  of  fig- 


I5O       UNITY  OF  NATURAL  PHENOMENA. 

ures  might  represent  exactly  their  double  conductibili- 
ty.  The  close  connection  existing  between  calorific 
and  electric  phenomena,  hardly  permits  us  to  hope  that 
the  mechanical  action  of  electricity  may  be  isolated  in 
practice,  or  reached  by  direct  observation. 


III. 

Electricity  and  Light  ;  their  Mutual  Relation. 

IN  the  degree  that  we  have  examined  the  peculiari- 
ties which  mark  the  propagation  of  the  currents,  the 
origin  of  the  electro-motor  forces,  and  the  distribu- 
tion of  work  in  the  conductors,  we  have  become  con- 
firmed in  the  idea  that  electricity  consists  in  a  trans- 
port of  the  ethereal  fluid,  of  the  same  fluid  that  pro- 
duces light. 

This  will,  indeed,  be  to  many  minds  a  resemblance 
hitherto  unexpected.  To  compare  light  and  electrici- 
ty is  quite  a  new  idea,  and  yet  we  have  just  been 
regarding  both  as  different  motions  of  the  same  fluid. 
Between  these  two  modes  of  motion  a  new  bond 
appears. 

If  we  look  at  the  generality  of  natural  objects,  we 
shall  notice  that  those  which  are  transparent  are 
usually  non-conductors ;  permeable  to  light,  they  re- 


ELECTRICITY.  151 

fuse  passage  to  electricity.,  On  the  other  hand, 
conductors  are  generally  opaque ;  witness  all  the 
metals. 

The  objection  may,  perhaps,  be  urged  that  water  is 
both  transparent  and  a  conductor ;  gutta-percha,  opaque 
and  a  non-conductor ;  but  let  us  consider  here  extreme 
cases  only,  neglecting  those  of  an  intermediate  char- 
acter. We  see,  then,  two  clearly  marked  general 
groups,  transparent  bodies  and  conductors.  These 
are  ill-chosen  designations,  since  they  convey  no  idea 
of  contrast  ;  but  beneath  the  terms  let  us  look  for 
the  facts.  Among  bodies  of  the  first  class,  the  ether 
moves  transversely  only  ;  on  the  other  hand,  it  can 
take  a  longitudinal  motion  only  in  bodies  of  the  sec- 
ond class.  Difference  of  molecular  aggregation  cre- 
ates, therefore,  a  difference  of  mobility  with  regard  to 
ether.  This  is  all  we  can  say  ;  but  we  may  assert 
that  the  two  classes  of  bodies  enclose  not  two  differ- 
ent fluids,  but  one  and  the  same  ether,  susceptible  of 
a  variety  of  motion. 

To  admit  the  existence  of  a  luminous  fluid  belonging 
to  transparent  bodies,  and  of  an  electric  fluid  peculiar 
to  conducting  bodies,  would  lead  to  very  strange  re- 
sults. 

When  lead  combines  with  silica  to  make  glass,  we 

»  * 

should  have  to  suppose  that  the  electric  fluid  is  driven 


152       UNITY  OF  NATURAL  PHENOMENA. 

away  and  replaced  by  the  luminous  fluid!  The  dia- 
mond in  becoming  charcoal,  is  no  longer  transparent 
and  non-conductor  ;  it  becomes  opaque  and  a  con- 
ductor. Here,  then,  would  be  another  change  of 
fluids.  Such  a  thing  cannot  be  conceived  as  possible. 
We  can,  on  the  contrary,  very  readily  imagine  how  a 
single  ethereal  fluid,  following  the  molecular  arrange- 
ment of  bodies,  may  sometimes  find  its  motion  ob- 
structed in  one  direction,  sometimes  in  the  other. 

We  will  here  add  an  argument  furnished  by  the 
velocities  with  which  light  and  electricity  are  propa- 
gated. The  velocity  of  light  is  about  one  hundred  and 
eighty-five  thousand  miles  a  second.  That  of  electrici- 
ty has  been  determined  with  far  less  exactness;  since  it 
depends  upon  the  nature  of  the  conductors,  and  a 
variety  of  circumstances  which  observers  have  not 
succeeded  in  eliminating.  But  taking  a  mean  between 
the  widely  different  results  yielded  by  experiments,  we 
shall  not  come  far  from  the  same  rate  of  one  hundred 
and  eighty-five*  thousand  miles  a  second. 

In  this  resemblance  may  be  seen  a  confirmation  of 
our  hypothesis.  It  should  not  in  the  least  surprise  us 
that  the  same  number  represents  two  velocities  cor- 
responding, in  our  view,  with  two  motions  of  the  same 
fluid  in  the  same  direction  ;  the  velocity  of  light  is,  in 


ELECTRICITY.  153 

fact,  that  of  the  longitudinal  impulse  from  which  the 
transversal  motions  result. 

Such  are  but  very  general  views  of  this  subject,  and 
it  can  hardly  be  said  that  we  see  clearly  the  connec- 
tion between  the  phenomena  of  light  and  of  electricity. 
Scarcely  can  we  conceive  of  the  conditions  capable 
of  effecting  this  twofold  faculty  of  motion  in  the 
ether. 

We  are  acquainted  with  the  ingenious  explanations 
Father  Secchi  had  recourse  to  in  order  to  show  how 
the  impulse  sent  along  a  luminous  ray  betrays  itself 
in  transverse  vibrations.  Other  hypotheses  have  been 
proposed  to  show  how  these  transversal  vibrations  can 
be  extinguished  in  conducting  bodies  to  the  advan- 
tage of  the  longitudinal  ones.  But  let  us  leave  these 
problems  in  their  obscurity,  —  it  is  quite  fitting  that 
we  should  conclude  our  hasty  view  of  the  phenomena 
of  electricity  with  an  avowal  of  the  uncertainty  of  our 
position.  These  phenomena  still  offer  much  that  is 
obscure,  and  it  is  only  in  keeping  with  the  actual  state 
.of  our  knowledge  that  we  dismiss  them,  leaving  im- 
portant questions  still  pending. 


154  UNITY    OF   NATURAL    PHENOMENA. 


CHAPTER  V. 
THE   ATTRACTIVE   FORCES. 

I. 

Points  of  Resemblance  and  of  Dissimilarity  presented 
by  Gravity ',  Cohesion,  and  Chemical  Affinity. 

THE  charcoal  points  of  an  electric  lamp  grow  hot, 
and  become  luminous,  when  a  current  passes  through 
them.  A  furnace  fire  gives  out  heat  and  work.  A  ray 
of  light  falling  upon  a  sensitive  plate  determines  an 
electro-motor  action,  which  becomes  motion  in  the 
needle  of  a  galvanometer,  heat  in  the  thermometric 
index.  We  might  multiply  to  infinity  similar  examples 
in  which  light,  heat,  and  electricity  appear  as  converti- 
ble phenomena,  or  reducible  to  the  idea  of  mechanical 
work.  Work  produces  them,  and  they  produce  work. 
They  originate  in  motion,  and  they  are  resolvable  into 
motion.  The  public  mind  is  accustomed  —  so,  at 
least,  it  seems  to  us  —  to  regard  in  this  manner  the 
effects  of  light,  heat,  and  electricity  ;  but  the  point  is 
not  so  well  settled  in  regard  to  the  attractive  forces, 


THE  ATTRACTIVE  FORCES.  155 

gravity,  cohesion,  and  affinity,  which  appear  to  reside 
in  the  recesses  of  matter.  Until  now  they  preserve  a 
more  mysterious  aspect.  It  remains  for  us  to  see  if 
we  shall  be  able  to  dissipate,  in  part,  the  obscurity 
which  surrounds  them  by  applying  the  principle  which 
now  enables  us  to  throw  light  on  all  natural  phe- 
nomena. 

In  the  progress  of  our  work  we  have  briefly  indi- 
cated, as  opportunity  offered,  the  considerations  which 
enable  us  to  reduce  these  forces  to  the  effects  of  mo- 
tion. We  have  especially,  then,  to  classify  and  de- 
velop here  the  hypotheses  previously  broached. 

In  the  first  place,  the  attractive  forces  should  not  be 
considered  as  inherent  in  matter. 

When  Newton  proclaimed  the  law  of  universal 
gravitation,  he  took  good  care  to  make  his  reservations 
in  regard  to  it.  After  having  described  the  planetary 
motions  in  his  book,  The  Mathematical  Principles  of 
Natural  Philosophy,  he  adds,  "I  have  thus  far  ex- 
plained celestial  phenomena  and  those  of  the  sea  by 
the  force  of  gravity  ;  but  I  have  nowhere  assigned  the 
cause  of  this  gravitation.  This  force  comes  from  some 
cause  which  penetrates  to  the  very  centre  of  the  sun 
and  planets,  without  losing  any  of  its  activity  ;  it  acts 
according  to  the  quantity  of  matter,  and  its  action  ex- 
tends in  all  directions  to  immense  distances,  always 


156        UNITY  OF  NATURAL  PHENOMENA. 

decreasing  in  the  inverse  ratio  of  the  square  of  the 
distances.  I  have  not  yet  been  able  to  deduce  from  the 
phenomena  the  reason  of  these  properties  of  gravity,  and 
I  do  not  conceive  of  any  hypothesis.  ...  It  is  enough 
that  gravity  exists  ;  that  it  acts  according  to  laws  that 
have  just  been  exposed  ;  and  that  it  can  explain  all  the 
motions  of  the  heavenly  bodies,  and  those  of  the  sea." 
Again,  in  the  same  book  he  says,  "  I  mean  by  the 
word  Attraction,  the  endeavor  which  bodies  make  to 
approach  each  other  ;  whether  this  endeavor  results 
from  the  action  of  bodies  which  mutually  seek  each 
other,  or  which  influence  each  other  by  means  of 
emanations,  or  whether  it  result  from  the  action  of 
the  ether,  of  the  air,  or  any  other  medium,  corporeal 
or  incorporeal,  which  urge  towards  each  other,  in 
some  way  or  other,  all  the  bodies  which  float  in 
them." 

Thus  Newton  left  this  question  undecided  ;  but  after 
him  it  became  gradually  a  custom  to  consider  gravity 
a  kind  of  quality  inherent  in  bodies.  Many  people 
admit  to-day,  as  a  primary  axiom,  that  matter  is  inert, 
and,  for  the  second,  that  it  attracts  according  to  such 
and  such  laws.  We  have  already  said  that  it  is  neces- 
sary to  choose  between  these  two  contradictory  ideas. 
If  the  molecules  are  drawn  towards  each  other  by 
virtue  of  a  cause  which  is  within  themselves,  how  can 


THE    ATTRACTIVE   FORCES.  I $? 

you  say  that  they  are  inert  ? ,  They  are  active,  on  the 
contrary,  and  all  the  structure  which  you  have  raised 
upon  the  idea  of  inertia  crumbles  to  its  foundation. 

What  will  be  the  case,  then,  if  we  pass  from  gravity 
to  chemical  affinity!  If  the  molecules  exercise  a 
choice  by  virtue  of  an  inherent  principle,  they  have, 
then,  a  primary,  active  principle  of  their  own  ;  they 
have  wills,  caprices  !  Chemistry  becomes  the  study 
of  the  molecular  passions.  We  shall  find  in  it  sym- 
pathies and  antipathies  ;  base  instincts  and  noble  sen- 
timents ;  lawful  affections  and  culpable  desires  ;  happy 
marriages  and  ill-assorted  unions  ;  half-concealed  quar- 
rels and  open  contests.  Such  are  the  idyls  and  the 
dramas  which  chemistry  presents  to  us  if  we  place  in 
the  molecules  a  repulsive  and  an  attractive  principle, 
as  formerly  a  spirit  of  good  and  a  spirit  of  evil  were 
made  to  dwell  in  human  souls. 

It  is  a  pure  geometrical  fiction  to  suppose  that  two 
molecules  act  upon  each  other  at  a  distance.  In 
reality  we  are  only  acquainted  with  actions  which  take 
place  by  contact,  by  the  communication  of  motion. 
Between  the  molecules  are  the  ethereal  atoms  ;  shocks 
are  transmitted  from  one  to  the  other  ;  the  matter  re- 
mains inert,  and  is  only  excited  to  motion  on  the  side 
where  it  is  struck.  The  repellent  forces  have  already 
disappeared  before  the  idea  of  calorific  motion  ;  the 


158       UNITY  OF  NATURAL  PHENOMENA. 

attractive  forces   must  likewise    be   reduced   to   the 
effects  of  impulse. 

When  we  compare  the  three  forces,  which  we  find 
grouped  in  the  same  family,  —  gravity,  cohesion,  and 
chemical  affinity,  —  we  are  at  once  struck  with  the 
disproportion  between  them. 

How  much  more  powerful  is  cohesion  than  gravity  ; 
an  iron  wire  will  not  break  under  its  own  weight  until 
it  reach  a  length  of  five  thousand  metres.  Enormous 
masses  of  metal  are  needed  to  overcome  by  their 
weight  the  cohesion  which  'exists  in  a  single  section 
of  the  wire. 

What  is  more  extraordinary  still  is,  that  when  once 
the  adhesion  is  overcome,  and  the  wire  broken,  the 
closest  contact  of  the  disjointed  parts  reproduces  no 
trace  of  the  primitive  cohesion.  Thus  cohesion,  in- 
comparably more  intense  than  weight,  is  sensible  only 
at  extremely  small  distances  ;  weight,  more  feeble,  on 
the  contrary,  continues  its  action  at  infinite  distances. 

If  any  one  is  desirous  of  getting  a  comparative  idea 
of  these  different  forces,  he  may  have  recourse  to  the 
following  hints.  They  are  due  to  a  learned  physicist, 
M.  Dupr6,  who  for  long  years  has  devoted  himself  to 
the  study  of  molecular  activities. 

M.  Duprd  deduced  from  his  experiments  and  calcu- 
lations the  force  necessary  to  overcome  the  mutual 


THE   ATTRACTIVE   FORCES.  1 59 

affinity  of  the  elements  of  water  ;  to  separate  by  force 
oxygen  and  hydrogen  over  the  surface  of  a  square  mil- 
limetre. He  found  this  force  would  be  about  sixteen 
hundred  and  seventy-three  kilogrammes. 

To  overcome  the  molecular  adhesion  of  water,  to 
tear  away  one  layer  from  its  neighbor,  a  force  would 
be  required  of  seventy  kilogrammes  to  the  square  mil- 
limetre.* 

Finally,  it  is  known  that  over  this  same  surface 
gravity  exerts  an  action  of  only  10.33  grammes. 

Comparing  the  three  numbers  which  represent  the 
power,  respectively,  of  affinity,  cohesion,  and  gravity, 
we  can  appreciate  the  enormous  difference  in  their 
values. 

II. 

Gravity  may  be  considered  as  an  Effect  of  the  Motions 
of  Ether  and  of  Ponderable  Matter. 

LET  us  attack,  without  further  delay,  the  theoretical 
considerations  which  may  enlighten  us  as  to  the  na- 
ture of  the  attractive  forces,  and  let  us  begin  with 
gravity. 

Let  us  imagine  the  ether  uniformly  diffused  through- 
out space.  Its  atoms,  endowed  with  motions  of  pro- 

*  That  is,  nearly  fifty  tons  to  the  square  inch !  —  Translator 


l6o        UNITY  OF  NATURAL  PHENOMENA. 

gression  and  rotation,  strike  each  other  in  the  manner 
already  mentioned. 

Let  us  now  suppose  that,  at  some  point  within, 
there  is  a  special  and  permanent  disturbing  cause, 
as,  for  example,  a  molecule  having  weight,  and  itself 
endowed  with  a  vibratory  motion.  The  shock  goes 
on,  extending  throughout  the  ethereal  mass,  and  by 
reason  of  the  nature  of  this  medium  is  propagated  in 
all  directions.  The  atoms  nearest  to  the  heavy  mole- 
cule will  receive  violent  shocks  ;  they  will  be  power- 
fully urged,  and  their  ranks  will  grow  thin  in  the 
neighborhood  of  the  centre  of  disturbance,  and  the 
layer  contiguous  to  the  molecule  will  become  less 
dense  than  the  rest  of  the  medium.  The  motor  action 
continuing,  this  same  effect  becomes  propagated  from 
layer  to  layer  throughout  space.  As  a  final  result, 
the  ether  becomes  arranged  around  the  centre  of  dis- 
turbance in  concentric  layers,  the  first  of  which,  and 
nearest  to  the  molecule,  will  be  least  dense,  and  they 
will  go  on  indefinitely  increasing  in  density.  This 
condition  of  things  might  be  easily  represented  and  the 
figure  traced  ;  the  molecule  at  the  centre,  around  it 
spheres  of  atoms,  wide  apart  at  first,  then  nearer  and 
nearer  to  each  other.  Let  us  remark  in  passing,  that 
the  difference  in  density  of  contiguous  layers,  like  all 
effects  which  are  propagated  by  concentric  spheres,  is 


THE  ATTRACTIVE  FORCES.          l6l 

inversely  proportional  to  the' surface  of  these  spheres, 
that  is,  to  the  square  of  their  radii. 

This  established,  suppose  a  second  molecule  to  be 
situated  at  any  point  of  this  system.  It  will  encoun- 
ter on  the  side  towards  the  first  molecular  layers  of 
ether  less  dense  than  upon  the  opposite  side  ;  pressed 
upon  by  the  ether  in  all  directions,  it  will  receive,  not- 
withstanding, fewer  shocks  on  the  side  towards  the 
first  molecule,  and  it  will  consequently  tend  to  move 
towards  it. 

Such  would  seem  to  be  the  cause  of  gravity. 

The  second  molecule  is  pushed  towards  the  first, 
because  it  encounters  ethereal  layers  of  different  den- 
sities, and  the  energy  of  this  action,  for  the  reason  we 
have  just  now  pointed  out,  is  inversely  proportional  to 
the  square  of  the  distance  between  the  two  molecules. 
In  this  statement  we  recognize  the  law  by  which 
gravity  acts. 

What  we  have  just  said  concerning  isolated  mole- 
cules, is  also  applicable  to  those  grouped  in  a  way  to 
form  a  body.  Such  a  group  will  effect  in  the  ether 
that  variation  of  density  we  have  described  ;  it  will 
effect  it  with  so  much  the  more  force  as  the  molecules 
are  more  numerous,  or  the  mass  of  the  body  greater. 
The  stars,  in  fact,  are  only  huge  bodies,  impelled  by  the 
same  cause  that  makes  heavy  substances  fall  to  the 
II 


1 62       UNITY  OF  NATURAL  PHENOMENA. 

surface  of  the  earth.     With  the  former,  as  with  the  lat- 
ter, the  attraction  is  only  that  tendency  to  approach, 

the  origin  of  which  we  just  now  referred  to  external 

t 
impulses. 

Of  course  the  brief  and  general  outlines  just  given 
do  not  constitute  an  exact  demonstration.  To  throw 
light  upon  a  question  of  such  high  importance,  it 
would  be  necessary  to  pursue  the  phenomena  into  their 
minutiae  ;  to  exhibit  in  detail  the^various  rebounds 
made  by  the  ether,  which  result  in  its  arrangement 
about  the  molecules  in  layers  of  different  density.  It 
would  be  necessary  to  anticipate  the  doubts  generated 
by  such  an  exhibit,  and  to  reply  to  the  principal  objec- 
tions that  might  be  offered. 

For  example,  it  might  be  asked  why  the  effect  we 
describe  is  peculiar  to  the  material  molecules  ;  why  it 
is  not  produced,  at  least  here  and  there,  around  the 
ethereal  atoms.  The  answer  to  this  is  easy.  In  the 
midst  of  the  ethereal  mass,  in  the  absence  of  any 
molecule,  everything  is  symmetrical  with  regard 
to  each  atom  ;  the  effect  begins,  if  you  please,  around 
each  of  the  atoms ;  it  is  as  if  it  did  not  begin  around 
any  of  them,  and  the  medium  remains  uniformly 
dense ;  to  break  its  uniformity,  there  is  needed  a 
centre  of  disturbance. 

It  will  be  asked,  again,  if  it  is  not  a  very  arbitrary 


THE  ATTRACTIVE  FORCES.          163 

supposition  to  give  to  atoms^and  especially  to  mole- 
cules, the  round  form  which  seems  necessary  at  the 
start,  in  order  to  explain  the  regularity  of  the  shocks 
and  the  symmetry  of  their  effects.  Here  again  the 
answer  is  easy.  The  theory  of  rotation  teaches,  in 
fact,  that  the  shocks  do  not  depend  upon  the  exterior 
form  of  the  bodies,  and  that  we  may  always  conceive 
of  a  solid,  of  any  form  whatever,  as  being  replaced  by 
an  ellipsoidal  globe.  The  round  form  is  not  then 
really  necessary,  either  to  the  molecules  or  even  to  the 
atoms. 

There  would  be  many  other  objections  to  overcome  ; 
but  it  is  easy  to  see  that  we  could  not  here  analyze  all 
the  circumstances  of  the  phenomenon.  Our  end  is 
attained  if  the  general  principle  of  the  explanation 
just  given  has  been  grasped,  and  if  it  is  seen  how  the 
motion  of  the  ether  may  produce  terrestrial  as  well  as 
sidereal  attraction. 

There  remains  a  point,  however,  upon  which  we 
cannot  help  saying  a  few  words. 

It  may  be  observed  that  modern  astronomy  is  con- 
structed independently  of  the  idea  of  the  ether.  It  is 
the  physicists  who,  first  through  their  studies  upon 
light,  then  through  the  inductions  drawn  from  them, 
have  imposed  upon  science  the  idea  of  this  universal 


164  UNITY    OF   NATURAL    PHENOMENA. 

fluid.*  It  may,  accordingly,  be  asked  if  this  idea  will 
not  be  found  in  disagreement  with  the  astronomical 
laws  that  have  been  established  without  it.  Those 
who  are  averse  to  admitting  the  existence  of  the  ether, 
do  not  fail  to  object  that  the  progress  of  the  stars 
must  be  retarded  by  this  fluid  ;  that  the  planets,  by 
reason  of  the  resistance  they  encounter,  must  con- 
stantly be  approaching  the  sun,  and  that  notwith- 
standing astronomers  find  no  symptom  of  such  an 
effect 

The  retardation  exists,  perhaps,  without  it  being 
possible  to  prove  it,  reply  the  partisans  of  the  ether. 

*  "  Whatever  the  eye  perceives  in  the  ether,  the  ear  perceives 
in  the  air;  whatever  the  ether  presents  to  our  organs  by  means 
of  colors,  the  air  presents  to  us  by  means  of  modulations  and 
sounds.  Thus  Nature  is  always  the  same,  always  similar  to  her- 
self, both  in  light  and  in  sound,  in  the  eye  and  in  the  ear;  the 
only  difference  is,  that  in  one  she  is  quicker  and  more  subtle,  and 
in  the  other  slower  and  more  gross,  exhibiting  herself  to  our 
various  senses  by  means  of  her  various  degrees  and  momenta, 
and  being  as  perceptible  to  sense  in  one  medium  as  she  is  in  an- 
other. How  admirable  are  the  varied  and  sportive  movements  of 
nature!  How  charming  and  delightful  does  she  render  herself 
solely  by  her  varieties  in  the  motions  of  her  elements,  being  as 
beautiful  in  the  ether  by  the  play  of  her  colors  as  she  is  harmo- 
nious in  the  air  by  the  modulations  of  her  sounds !  What  grati- 
fications does  she  afford  to  us  in  the  diversified  operations  of  her 
living  machinery!  " —  Sivedenborg,  Principia,  vol.  ii.  p.  309. 

For  a  full  and  interesting  account  of  the.luminiferous  ether, 
the  reader  is  referred  to  the  above-mentioned  work. 


THE   ATTRACTIVE   FORCES.  1 6$ 

If  we  enter  the  domain  of  facets,  we  are  convinced  that 
this  retardation  can  only  be  very  feeble,  on  account  of 
the  tenuity  of  the  fluid  which  produces  it.  Calcula- 
tions have  been  established,  according  to  which  the 
resistance  of  the  ether  would  shorten,  by  three  meters 
a  year,  the  distance  of  the  earth  from  the  sun  ;  the 
duration  of  the  year  would  .thus  be  shortened  one 
second  in  six  thousand  years.  The  state  of  our  as- 
tronomical observations  does  not  allow  the  singling 
out  of  such  a  consequence  from  the  midst  of  the  per- 
turbations of  the  terrestrial  orbit  already  known. 

Failing  of  any  decisive  facts  in  the  planetary  mo- 
tions, the  controversy  is  thrown  back  upon  the  com- 
ets. If  the  ethereal  resistance  is  insensible  for  the 
planets  by  reason  of  their  great  density,  it  must  be 
appreciable  for  the  comets,  which  have,  so  to  speak,  no 
mass,  and  which  have  been  termed  visible  nothings* 


*  It  is  not  very  long  since  the  extreme  tenuity  of  cometary 
matter  has  been  established.  Formerly  the  shock  of  these  bodies 
was  always  considered  dangerous  for  the  planets.  It  is  to  a  shock 
of  this  character  that  Buffon  attributed  the  origin  of  our  plane- 
tary system  ;  a  comet  precipitating  itself  into  the  sun,  had  de- 
tached fragments  of  matter  from  it,  and  hurled  them  into  space. 
Again,  it  is  to  shocks  of  this  kind  that  various  geologists  attrib- 
ute the  terrestrial  cataclysms;  comets,  coming  in  contact  with 
the  earth,  would  have  displaced  the  axis  of  rotation  and  deter- 
mined the  great  deluges.  Such  opinions  no  longer  exist.  Com- 
ets are  regarded  to-day  as  quite  inoffensive  heavenly  bodies,  in- 


1 66  UNITY   OF   NATURAL   PHENOMENA. 

Here  a  consideration  comes  in  to  obscure  the  problem. 
The  extreme  lightness  of  the  comets  must  render 
them  sensible  to  the  resistance  of  a  universal  medium 
undoubtedly ;  but  it  exposes  them  also  to  perturba- 
tions of  other  sorts.  They  are  powerfully  deviated 
from  their  course  when  they  pass  in  the  neighborhood 
of  the  planetary  bodies.  When  Lexell's  comet,  in 
1770,  passed  through  the  satellites  of  Jupiter,  the  time 
of  its  revolution  became  abruptly  shortened  from  fifty 
years  to  five  and  a  half  years.  How  discern  the  in- 
fluence of  the  ether  in  the  midst  of  pertubations  of 
this  kind  ?  Encke's  comet,  whose  periodicity  has 
been  known  since  1818,  has  a  revolution  of  very 
short  duration,  about  three  and  a  quarter  years ;  its 
orbit  lies  entirely  within  that  of  Jupiter.  In  compar- 
ing its  successive  appearances  since  1818,  there  has 
been  observed  a  gradual  diminution  in  the  time  of  its 
revolution.  It  has  been  proved,  moreover,  that  this 
effect  does  not  proceed  from  the  perturbing  influence 

capable  of  disturbing  the  peace  of  the  world.  They  have  been 
seen  to  pass  close  by  planets  without  causing  any  disorder  in 
them.  Twice  has  LexelFs  comet  been  seen  to  rush  through  the 
satellites  of  Jupiter,  without  producing  any  derangement  in  them. 
According  to  the  recent  calculations  of  M.  Faye,  the  nucleus  of 
comets,  which  is  the  most  compact  portion,  is  scarcely  nine  times 
more  dense  than  the  air  which  remains  in  our  pneumatic  ma- 
chines after  we  have  made  the  vacuum  as  complete  as  possible; 
as  to  the  density  of  the  tail,  it  would  be  ten  billion  times  less. 


THE  ATTRACTIVE  FORCES.  l6/ 

of  the  planets.  Certain  astronomers  have  concluded 
from  this  that  it  must  be  attributed  to  the  resistance 
of  a  medium,  and  have  there  seen  the  first  astronomi- 
cal demonstration  of  the  existence  of  the  ether  ;  but 
this  conclusion,  drawn  from  a  solitary  example,  in  the 
midst  of,  the  uncertainty  still  hanging  over  the  greater 
part  of  the  particulars  of  cometary  motion,  cannot  be 
regarded  as  very  binding. 

Thus  astronomical  observations  furnish  no  charac- 
teristic fact  upon  the  subject  of  the  resistance  of  a 
medium,  and  no  conclusion  in  regard  to  it  is  to  be 
drawn  either  from  the  course  of  the  planets  or  that  of 
the  comets.  But  we  have  now  to  ask  ourselves  if  the 
explanation  just  given  upon  the  subject  of  the  origin 
of  attraction  does  not  illuminate  the  problem  with 
an  entirely  new  light  ? 

Mathematical  analysis  refers  to  two  forces  as  the 
causes  which  produce  the  curvilinear  motion  of  the 
stars.  One,  the  initial  force  of  impulsion  or  ac- 
quired velocity,  tends  to  direct  them  in  a  straight  line, 
while  gravity  incessantly  deviates  them  from  this 
course.  This  is  that  dynamic  equilibrium,  established 
by  astronomers  independently  of  any  notion  of  the 
ether,  which  seemed  to  be  compromised  when  the 
physicists  admitted  the  existence  of  a  universal  medi- 


1 68       UNITY  OF  NATURAL  PHENOMENA. 

um ;  the  ether  must  needs  derange  this  balancing  of 
two  forces  instituted  without  its  aid. 

If  now  we  recognize  the  ether  as  the  origin  of  at 
least  one  of  the  two  forces,  the  question  changes  its 
aspect.  It  may  no  longer  be  said  that  it  has  remained 
foreign  to  the  establishment  of  the  equilibrium  of  the 
heavenly  bodies  ;  on  the  contrary,  we  find  that  we 
have  unwittingly  forced  it  to  take  part  in  this  equi- 
librium. Henceforward .  let  us  no  longer  speak  of  a 
new  resistance  introduced  by  the  ether  !  Its  mode  of 
resisting  the  celestial  motions  is  precisely  to  deter- 
mine the  attraction,  and  so  influence  the  course  of 
the  stars.  We  say  that  the  ether  produces  gravity ; 
that  it  urges  the  heavenly  bodies  in  a  certain  direc- 
tion ;  by  so  doing  we  have  accounted  for  all  the  ac- 
tions which  it  exercises,  for  the  shocks  it  gives  upon 
all  sides.  It  would  be  a  double  task  to  introduce  a 
second  time  into  our  calculations,  under  the  form  of 
resistance  to  motion,  the  shocks  which  the  stars  re- 
ceive from  the  direction  in  which  they  move. 

If  this  is  so,  if  it  is  true  to  say  that  the  ether  can- 
not be  considered  at  the  same  time  as  a  cause  of  side- 
real motion,  and  an  obstacle  to  this  motion,  we  need 
no  longer  be  surprised  that  astronomy  finds  in  no  part 
of  the  heavens  the  mark  of  a  resisting  medium. 


'THE   ATTRACTIVE   FORCES.  169 


III. 

Historical  Notions   regarding  the  Idea  of  Universal 
Attraction. 

IT  is  possible,  then,  to  bring  within  the  compass  of 
our  hypothesis  the  cause  which  produces  the  gravity  of 
bodies  ;  but  this,  we  cannot  disguise  it,  is  one  of  the 
most  difficult  points  we  have  to  treat.  Such  is  the 
power  of  habit  over  our  minds,  that  the  origin  of  attrac- 
tion would  seem  to  us  unattainable.  To  connect  this 
conception  with  a  more  general  idea  seems  a  chimeri- 
cal undertaking.  In  order  to  support  the  demon- 
stration we  have  attempted  in  regard  to  this,  it  will 
not  be  without  use  to  give  a  slight  sketch  of  the  way 
in  which  this  grand  idea  of  universal  attraction  had 
its  birth,  and  how  it  has  been  developed.'  By  indica- 
ting the  role  which  it  has  played  in  the  history  of  our 
sciences,  we  shall  better  mark  the  place  which  it 
should  hold  in  the  physical  science  of  our  day.  In 
beholding  how  the  human  mind  has  attained  to  a  law 
so  high,  it  will  seem  to  us  possible  for  it  to  go  higher 
yet,  and  that  gravity,  in  order  to  have  explained  so 
many  things,  cannot  itself  be  inexplicable. 

Modern  astronomy  begins  with  the  book  of  the 
Revolutions  of  the  Heavenly  Bodies,  which  Coper- 


I7O       UNITY  OF  NATURAL  PHENOMENA. 

nicus  published  in  1543.  Copernicus,  overturning  the 
doctrine  of  Ptolemy,  placed  the  sun  in  the  centre  of 
the  universe.  Around  this  body  he  made  revolve  the 
six  planets  then  known,  Mercury,  Venus,  the  Earth, 
Mars,  Jupiter,  and  Saturn,  and  he  endowed  them  also 
with  a  motion  of  rotation  upon  their  axes. 

Although  dedicated  to  Pope  Paul  III.,  the  book  of 
the  Revolutions  of  the  Heavenly  Bodies  was  con- 
demned, as  contrary  to  the  text  of  the  Scriptures. 

Whether  he  desired  to  escape  the  censures  of  the 
Roman  court,  or  whether  he  had  the  ambition  to  at- 
tach his  name  to  a  system  which  was  peculiar  to  him- 
self, Tycho-Brahe  adopted  an  eclectic  hypothesis.  He 
deprived  the  earth  of  its  double  motion,  and  made  the 
moon  and  the  sun  revolve  around  it,  conformably  to 
the  doctrine  of  Ptolemy ;  but  he  admitted  at  the  same 
time  the  revolution  of  Mercury,  Venus,  Mars,  Jupiter, 
and  Saturn  around  the  sun.  In  spite  of  this  whimsi- 
cal theory,  Tycho-Brahe  is  one  of  the  founders  of  the 
science  of  the  heavens.  Assisted  by  his  disciples  and 
numerous  colaborers  in  the  little  astronomical  city 
which  he  had  founded,  he  searched  the  heavens  in 
all  directions,  and  accumulated  upon  the  subject  of 
the  planetary  motions  a  prodigious  quantity  of  ob- 
servations, which  served  as  a  basis  for  the  labors  of 
Kepler. 


THE  ATTRACTIVE  FORCES.          I/I 

The  three  great  laws  to  which  Kepler  has  given  his 
name  are  well  known. 

Copernicus  and  Tycho-Brahe  had  preserved  the 
faith  of  the  ancients,  who  regarded  the  course  of  the 
planets  as  circular.  It  was  upon  this  opinion  that  the 
attention  of  Kepler  was  first  brought  to  bear.  Com- 
paring the  observations  of  Tycho  upon  the  motions  of 
the  planet  Mars  with  those  which  he  had  himself 
made,  he  convinced  himself  that  the  orbit  of  this  star 
was  not  circular ;  after  having  vainly  tried  several 
hypotheses,  he  finally  discovered  that  he  could  satis- 
fy the  result  of  his  calculations  by  supposing  that 
the  orbit  of  Mars  was  an  ellipse,  one  focus  of  which 
was  occupied  by  the  sun.  At  the  same  time  he  found 
that  the  areas  described  around  the  focus  by  the 
radius  vector  are  equal  in  equal  times.  Such  are 
the  two  first  laws  pointed  out  by  Kepler.  After  hav- 
ing verified  them  upon  several  planets,  he  published 
them  in  1609,  in  a  memoir  entitled,  De  motibus  stellcz 
Martis. 

The  third  law  is,  that  the  squares  of  the  times  of 
the  planetary  revolutions  are  proportional  to  the 
cubes  of  the  long  axes  of  the  orbits.  It  is  this  which 
cost  the  highest  efforts  of  Kepler's  persevering  genius. 
The  manner  in  which  he  announces  this  in  his  trea- 
tise, Harmonicas  Mundi,  partakes  of  the  enthusiasm 


172       UNITY  OF  NATURAL  PHENOMENA. 

which  such  a  discovery  caused  him.  "  After  having 
found,"  he  says,  "  the  true  dimensions  of  the  orbits 
through  the  observations  of  Brahe,  by  a  long-contin- 
ued and  laborious  effort,  I  have  at  length  discovered 
the  proportion  of  the  periodic  times  to  the  extent  of 
these  orbits.  And  if  you  wish  to  know  the  exact  date 
(of  this  discovery),  it  was  the  8th  of  March,  this  very 
year,  1618,  that,  first  conceived  in  my  mind,  then  un- 
skilfully attempted  in  figures,  hence  rejected  as  false, 
afterwards  reproduced  the  i$th  of  May,  with  a  new 
energy,  it  surmounted  the  darkness  of  my  intelligence, 
and  so  fully  confirmed  was  I  in  it  by  my  labor  of  sev- 
enteen years  upon  the  observations  of  Brahe,  and  from 
my  own  researches,  that  I  first  believed  that  I  was 
dreaming.  .  .  .  But  there  is  no  longer  any  doubt ; 
it  is  a  very  sure  and  very  exact  proposition,  that  the 
ratio  between  the  periodic  times  of  two  planets  is 
precisely  sesquialter  to  the  ratio  of  the  mean  dis- 
tance."* 

Thus  Kepler  had  determined,  in  three  truly  great 
laws,  the  orbits  of  the  planets  and  the  conditions  of 
their  motion.  He  was  so  near  the  principle  from 
which  these  laws  are  derived,  that  it  may  be  asked  if 

*  Half  the  long  axis  of  a  planetary  orbit  is  often  called  the 
mean  distance.  It  is,  in  fact,  the  mean  between  the  greatest  and 
least  distance  of  the  planet  from  the  sun. 


THE   ATTRACTIVE   FORCES.  1 73 

he  did  not  foresee  it.  End6wed  with  an  ardent  im- 
agination, he  naturally  sought  the  cause  of  these  mo- 
tions, the  nature  of  which  he  had  discovered  ;  but  in 
this  relation  his  works  show  us  hardly  more  than  the 
exuberance  of  ancient  astrological  fancies.  The  old 
Pythagorean  theories,  the  mysterious  properties  of 
numbers,  here  play  a  singular  part ;  and  one  is  aston- 
ished at  the  odd  dreams  which  are  mingled  with  the 
most  serious  calculations.* 

He  had,  nevertheless,  his  theory  upon  solar  attrac- 
tion. He  gave  to  the  sun  a  movement  of  rotation 
upon  an  axis  perpendicular  to  the  ecliptic,  thus  fore- 
seeing a- truth  which  experience  was  only  to  prove 
somewhat  later ;  immaterial  forces  emanating  from 
this  luminary  in  the  plane  of  its  equator,  endowed 
with  an  activity  decreasing  in  proportion  to  the  dis- 
tances, caused  each  planet  to  participate  in  this  circular 
motion.  The  planet,  carried  along  by  this  transcen- 
dent effluence,  followed  the  rotation  of  the  sun,  and  at 
the  same  time,  by  a  sort  of  instinct  or  magnetism,  it 

*  Yet  it  was  this  mystical  part  of  Kepler'  s  opinions,  this  be- 
lief in  the  mysterious  properties  of  numbers,  that  led  to  a  con- 
viction, on  his  part,  of  a  physical  connection  between  the  differ- 
ent parts  of  the  universe,  and  finally  to  the  discovery  of  those 
numerical  and  geometrical  laws  which  govern  them.  —  Trans- 
lator, 


UNITY  OF  NATURAL  PHENOMENA. 

alternately  approached  and  receded  from  the  central 
luminary,  sometimes  rising  above  the  solar  equator, 
and  sometimes  sinking  below  it. 

At  the  same  time  that  Kepler  was  determining  the 
constitution  of  planetary  motion,  Galileo  discovered 
the  law  of  the  acceleration  of  bodies  which  fall  freely 
to  the  ground,  or  which  glide  over  inclined  planes  ;  he 
established  the  general  properties  of  a  uniformly  ac- 
celerated motion. 

The  laws  of  gravity  at  the  surface  of  the  earth  con- 
stitute the  fundamental  principles  of  mechanics.  Ere 
long  Huyghens  perfected  the  theory  of  the  pendulum, 
and  gave,  through  his  Theory  of  Central  Forces  in  the 
Circle,  brilliant  suggestions  concerning  centrifugal 
force. 

Such  are  the  principal  elements  from  which  Newton 
derived  the  grand  discovery  of  universal  attraction. 
The  methods  of  calculation  had  also  just  been  en- 
riched by  some  remarkable  inventions.  Descartes  had 
founded  the  analytical  geometry,  and  Fermat  had 
just  laid  the  principles  of  the  infinitesimal  calculus. 
Thus  the  labors  of  a  half  century,  fruitful  in  great 
geometricians  and  great  astronomers,  concurred  in 
bringing  together  the  materials  which  Newton  was 
able  to  employ. 

Tradition  relates  that  Newton,  while  in  retirement 


THE    ATTRACTIVE   FORCES.  1/5 

in  the  country,  during  the  yeaV  1666,  saw  an  apple  fall 
from  a  tree.  Thereupon  directing  his  thoughts  to  the 
system  of  the  universe,  he  conceived  the  idea  that  the 
force  which  attracted  bodies  towards  the  surface  of  the 
earth  was  the  one  which  made  the  moon  turn  around 
the  earth,  and  the  planets  around  the  sun. 

Kepler's  laws  furnished  him  with  admirable  data, 
from  which  he  drew  the  consequences  resulting  from 
their  analysis.  From  the  law  of  the  proportion  be- 
tween the  areas  and  the  times,  he  concluded  that  every 
planet  is  submitted  to  an  attraction  constantly  directed 
towards  the  sun.  From  the  elliptical  motion,  he  con- 
cluded that  for  the  same  planet  the  tendency  towards 
the  sun  varies  from  one  point  to  another  of  the  orbit 
in  the  inverse  ratio  of  the  squares  of  the  distances. 
He  had,  then,  the  means  of  comparing  the  gravitation 
of  any  one  planet  towards  the  sun  in  any  two  points 
of  its  orbit ;  but  this  was  not  sufficient  ;  it  was  neces- 
sary, besides,  to  know  how  to  compare  the  gravitation 
of  two  different  planets,  for  it  might  be  that,  passing 
from  one  planet  to  the  other,  there  would  be  a  change 
in  the  amount  of  attraction.  The  third  law  of  Kep- 
ler, the  proportion  between  the  squares  of  the  times 
and  the  cubes  of  the  mean  distances,  permitted  New- 
ton to  complete  his  theory,  and  to  refer  all  these  at- 
tractions to  one.  This  law  signified,  in  fact,  that  all 


UNITY  OF  NATURAL  PHENOMENA. 

the  planets,  of  the  same  mass  and  at  equal  distances, 
would  be  equally  attracted  by  the  sun.  The  same 
equality  of  gravity  exists  in  all  the  systems  of  satellites, 
and  Newton  assured  himself  of  it  in  the  case  of  the 
moon,  as  well  as  in  that  of  the  satellites  of  Jupiter. 

It  was  with  the  lunar  attraction  that  he  began  the 
verification  of  his  theory.  The  question  was  to  deter- 
mine whether  the  force  which  incessantly  deviates  the 
moon  towards  the  earth  be  identical  with  terrestrial 
gravity.  In  this  case,  the  action  of  these  forces  re- 
ferred to  the  centre  of  the  earth  would  have  to  be  in 
the  ratio  of  the  earth's  radius,  taken  for  unity,  to  the 
square  of  the  distance  separating  the  two  heavenly 
bodies.  Newton  undertook  this  verification,  starting 
with  the  experiments  of  Galileo  upon  heavy  bodies ; 
but  there  existed  then  only  an  inexact  measurement 
of  the  earth's  radius,  and  the  great  geometrician  saw 
the  result  of  his  calculation  in  disagreement  with  his 
hypothesis.  Thereupon,  persuaded  that  unknown 
forces  were  joined  to  the  moon's  gravity,  he  gave  up 
for  a  time  his  ideas.  Some  years  later,  the  Academy 
of  Sciences  having  just  effected  the  measurement  in 
France  of  a  degree  of  the  meridian,  and  a  new  meas- 
ure of  the  earth's  radius  having  resulted  from  this 
work,  Newton  recommenced  his  researches,  and  this 
time  he  found  that  the  moon  was  retained  in  its  orbit 


THE    ATTRACTIVE   FORCES. 

by  the  sole  power  of  gravity'  The  sight  of  this  re- 
sult, of  which  he  had  despaired,  caused  him,  so  say  his 
biographers,  so  lively  an  excitement  that  he  could  not 
verify  his  calculation,  and  was  obliged  to  trust  the 
care  of  it  to  a  friend. 

Thus  one  and  the  same  law,  a  law  unique  and  grand, 
explained  all  the  motions  of  bodies  on  the  surface  of 
the  planets,  and  those  of  the  stars  in  space.  The 
principal  developments  of  this  law  were  collected  in 
the  immortal  treatise,  the  Mathematical  Principles, 
which  Newton  published  towards  the  close  of  the 
year  1687. 

Having  reached  a  principle  which  embraced  the 
universe  entire,  Newton  himself  made  brilliant  appli- 
cations of  it.  He  proved  that  the  earth  in  its  rotation 
must  become  flattened  at  the  poles,  and  he  determined 
the  amount  of  variation  in  the  length  of  the  degrees 
of  the  meridian.  He  saw  that  the  attractions  of  the 
sun  and  moon  give  rise  to,  and  maintain  in  the  sea, 
those  oscillations  which  constitute  its  ebb  and  flow. 
He  demonstrated,  finally,  the  mode  in  which  the 
spheroidicity  of  the  earth  at  the  equator  and  the 
inclination  of  the  polar  axis  to  the  ecliptic  determine 
the  phenomenon  of  the  precession  of  the  equinoxes. 
He  recognized,  in  a  general  way,  even  with  exactness 
upon  some  points,  the  perturbations  which  affect  the 

12 


178       UNITY  OF  NATURAL  PHENOMENA. 

planetary  system.  If  a  single  planet  be  considered  as 
gravitating  towards  the  centre  of  the  sun,  it  must  obey 
strictly  the  laws  of  Kepler  ;  but  this  is  no  longer  the 
case  when  it  concerns  the  attraction  of  several  of  the 
heavenly  bodies  towards  each  other,  if  instead  of 
two  bodies  there  be  three.  The  conditions  are  then 
changed  and  complicated,  even  so  far  as  to  become 
amenable  to  analysis  only  with  great  difficulty.  New- 
ton assigned  the  meaning,  and  sometimes  the  numeri- 
cal value,  of  several  of  the  planetary  perturbations,  thus 
tracing  in  their  germ  the  methods  which  were  in  our 
day  to  make  it  possible  for  mathematical  calculation 
to  find  the  planet  Neptune  at  the  extremity  of  the 
solar  system.  He  recognized  those  disturbing  phe- 
nomena which  affect  the  elements  of  the  planetary 
orbits,  and  which  astronomy  divides  into  two  cate- 
gories, the  secular  inequalities  at  very  long  intervals, 
and  the  periodic  inequalities,  the  period  of  which  is 
only  some  years. 

But  when  he  saw  that  the  planetary  ellipses  succes- 
sively approached  and  receded  from  the  circular  form ; 
that  their  orbits  did  not  always  remain  equally  inclined 
to  a  fixed  plane  ;  that  they  cut  the  ecliptic  according 
to  lines  which  changed  their  position  in  space,  a  dis- 
couraging thought  entered  his  spirit.  It  seemed  to  him 
that  the  feeble 'values  of  all  these  variations,  accumu- 


THE   ATTRACTIVE   FORCES. 

lating  in  the  course  of  centuries,  must  overturn  the 
system  of  the  universe.  He  declared  that  this  system 
did  not  possess  the  lasting  elements  of  preservation, 
and  that  it  would  be  necessary  for  a  transcendent 
power  to  intervene  from  time  to  time  to  repair  the 
disorder. 

Leibnitz  eagerly  opposed  such  an  opinion,  and  ridi- 
culed this  faith  in  an  intermittent  miracle.  Newton 
retorted  with  railleries  upon  the  subject  of  the  doctrine 
of  the  pre-established  harmony,  which  was,  it  must  be 
confessed,  one  of  the  oddest  conceptions  of  meta- 
physics. The  quarrel  soon  became  bitter,  and  was 
complicated  with  the  sharp  dispute  in  which  were  seen 
these  two  great  minds  contending  for  the  invention  of 
the  differential  calculus. 

Newton  had  traced  out  a  sublime  draught  of  the 
theory  of  sidereal  motion  ;  but  it  was  merely  a  draught. 
It  was  necessary  for  mathematical  analysis  to  accom- 
plish prodigies  ;  it  was  necessary  for  Euler,  Clairaut, 
D'Alembert,  Lagrange,  and  Laplace  to  amass  their 
efforts,  that  the  sketch  might  become  a  completed 
design. 

Clairaut  first  gave  a  complete  and  satisfactory  solu- 
tion of  the  problem  of  the  three  bodies,  which  consists 
in  determining  the  course  of  a  planet  subjected  to  the 
combined  attractions  of  two  other  heavenly  bodies. 


l8o       UNITY  OF  NATURAL  PHENOMENA. 

There  continued  to  be  an  uneasiness  in  regard  to 
the  astronomical  perturbations  whose  periodicity  was 
unknown.  It  was  Laplace  who  first  discovered  in 
them  an  evidence  sufficient  to  reassure  us  as  to  the 
conservation  of  the  planetary  system.  In  the  midst 
of  perturbations  of  every  kind  which  observation  made 
known,  there  was  a  quantity  which  remained  constant, 
or  which  at  least  was  only  subject  to  but  slight  period- 
ical variations.  This  was  the  major  axis  of  each  orbit, 
upon  which  depends,  according  to  the  third  law  of 
Kepler,  the  time  of  revolution  of  each  planet.  The 
solar  system  became,  as  it  were,  confirmed,  and  it  was 
seen  that  it  only  oscillated  about  a  mean  condition, 
from  which  it  never  departed  save  by  very  small 
quantities. 

Scarcely  had  this  result  been  obtained  when  it 
seemed  to  be  compromised.  Constant  inequalities 
were  pointed  out  in  the  journeys  of  Jupiter  and  Saturn. 
Comparing  ancient  observations  with  modern,  it  was 
found  that  the  motion  of  Jupiter  was  constantly  accel- 
erating, and  that  of  Saturn  was  subject  to  a  gradual 
retardation.  The  theoretical  consequence  of  these 
facts  was  of  a  character  to  strike  attention.  It  was 
necessary  to  conclude  from  them  that  Jupiter  would 
gradually  approach  the  sun,  and  finally  cast  himself 
into  it.  Saturn,  on  the  contrary,  was  destined  to  be- 


THE  ATTRACTIVE  FORCES.  iSl 

come  farther  and  farther  removed  from  the  centre  of 
our  system,  and  to  plunge  forever  into  the -darkness  of 
the  space  which  our  telescopes  do  not  reach.  The 
Academy  of  Sciences  was  disturbed  at  these  possible 
results  ;  it  summoned  to  this  question  the  labors  of  the 
geometricians.  Euler  and  Lagrange  descended  into  the 
arena,  without  solving  the  difficulty  ;  it  was  again  the 
sagacious  analysis  of  Laplace  which  demonstrated,  in 
the  reciprocal  perturbations  of  Jupiter  and  Saturn,  the 
reason  of  the  anomalies  pointed  out  by  observers,  and 
which  explained  them  by  an  inequality  of  long  period, 
the  development  of  which  demands  more  than  nine 
hundred  years. 

There  were  observed,  moreover,  inequalities  whose 
period  was  still  longer  ;  those  which  depend  upon  the 
precession  of  the  equinoxes  have  a  duration  of  ten 
hundred  and  sixty  centuries  ;  the  eccentricity  of  the 
earth's  orbit  goes  on  diminishing  from  the  most  remote 
ages,  obeying  a  period  whose  duration  is  reckoned 
neither  by  hundreds  nor  by  thousands  of  years,  —  a 
duration  of  time,  in  which  the  history  of  astronomical 
observations,  that  even  of  the  human  race,  figure  but 
as  a  point. 

We  have  now  followed  the  Newtonian  idea  up  to  the 
time  when  it  accounted  for  all  the  celestial  phenomena ; 
but  it  must  not  be  thought  that  this  idea  was  accepted 


1 82       UNITY  OF  NATURAL  PHENOMENA. 

at  once  by  all  minds.  Its  beginnings  were  marked  by 
the  liveliest  disputes.  The  quarrel  between  Cartesian- 
ism  and  Newtonianism  filled  all  the  first  half  of  the 
eighteenth  century. 

The  system  of  physics  of  Descartes  yielded  but 
slowly  before  that  of  Newton,  and  in  the  domain  of 
facts  itself  the  supremacy  between  the  two  doctrines 
remained  for  a  long  time  undecided.  Not-  the  synthe- 
sis only,  which  Newton  had  drawn  from  Kepler's  laws, 
but  those  very  laws  themselves  were  for  a  long  time  dis- 
puted. At  the  close  of  the  seventeenth  century,  Dom- 
inique Cassini  proposed  to  substitute  for  the  ellipses  of 
Kepler  a  curve,  which  seemed  to  be  more  accurately 
adapted  to  the  sidereal  motions  ;  this  curve  has  taken 
the  name  of  the  Cassinoid*  One  of  the  first  conse- 
quences of  Newton's  theory,  the  flattening  of  the  earth 
towards  the  poles,  was  denied.  The  sons  of  Cassini, 
heirs  of  the  paternal  traditions,  proved  by  the  measure- 
ment of  an  .arc  of  the  meridian  that  the  earth  was  a 
spheroid,  elongated  in  the  direction  of  its  axis.  This 
opinion  prevailed  in  our  Academy  of  Sciences  up  to 
the  time  when  an  expedition  was  organized  for  deter- 

*  In  the  ellipse,  the  sum  of  the  radii  drawn  from  a  point  of  the 
curve  to  the  two  foci  is  constant.  In  the  Cassinoid,  a  curve  of  the 
fourth  degree,  it  is  the  product  of  the  two  radii,  which  is  con- 
stant. 


THE   ATTRACTIVE   FORCES.  183 

mining  the  comparative  lengths  of  a  degree  near  the 
pole  and  near  the  equator.  Bouguer  and  La  Con- 
damine  set  out  in  1735  for  Peru  ;  Maupertius  and 
Clairaut  betook  themselves  to  Lapland.  The  hy- 
pothesis of  Newton  came  out  of  this  trial  victoriously, 
and  towards  1 744  the  greater  number  of  savants,  in- 
cluding the  two  Cassini  themselves,  recognized  the 
errors  in  the  experiment  or  reasoning  which  had  made 
them  take  the  earth  for  an  elongated  spheroid.  Then 
it  was  that  Descartes'  system  of  physics  was  finally 
overturned,  together  with  a  great  part  of  his  meta- 
physics, and  the  Newtonian  idea,  popularized  by  Vol- 
taire, and  afterwards  by  the  Encyclopedists,  remained 
triumphant. 

But,  if  we  are  going  to  the  bottom  of  things,  what 
was  the  point  especially  discussed  between  the  Carte- 
sians and  the  disciples  of  Newton  ? 

Descartes  set  out  with  this  principle,  that  the  whole 
universe  is  to  be  explained  by  motion,  and  we,  at  least; 
shall  not  make  this  a  reproach  against  him ;  it  is  upon 
this  very  stand-point  that  contemporary  science  places 
herself,  and  the  majority  of  our  physicists,  whether 
they  will  or  no,  are  found  to  be  Cartesians  in  this 
respect.  But  Descartes,  his  principle  laid  down,  with- 
out facts,  without  observations,  without  experiments, 
without  proof  of  any  sort,  by  a  pure  conception  of  his 


184       UNITY  OF  NATURAL  PHENOMENA. 

mind,  had  created  a  system  of  the  universe  ;  the  uni- 
verse, was  full  of  matter,  absolutely  full,  without  any 
void  ;  vast  circular  currents  existed  throughout  this 
matter,  and  carried  along  with  them  the  planets,  as  the 
current  of  a  river  carries  vessels  along.  The  disciples 
of  Descartes  abated  nothing  from  the  idea  of  .their 
master,  and  they  heaped  up  laborious  explanations  in 
order  to  show  how  the  vortices  could  be  propagated 
in  a  space  absolutely  full ;  how  the  particles  of  matter 
could  glide  over  each  other  without  any  interstitial 
vacuum. 

To  confront  this  doctrine,  Newton  brought  forward 
the  law  of  universal  gravitation  ;  this  law  contained  in 
itself  an  enormous  mass  of  facts.  Not  only  did  it 
explain  all  that  were  already  known,  but  it  fore- 
shadowed new  ones,  and  experiment  justified  these 
foreshadowings.  The  Newtonians  then  felt  them- 
selves upon  very  solid  ground.  In  their  enthusiasm 
'they  left  the  domain  of  facts,  and  came  to  look  upon 
gravity  as  a  mysterious  cause,  of  an  order  superior  to 
all  physical  phenomena.  Newton,  as  we  have  just  now 
shown,  guarded  himself  from  this  excess,  at  least  in 
the  beginning  of  his  career,  and  in  the  book  of  Princi- 
ples. Perhaps  he  was  less  reserved  in  this  respect  in 
his  old  age.  As  to  his "  followers,  they  had  an  evident 


THE  ATTRACTIVE  FORCES.          185 

i 

tendency  to  believe  themselves  in  possession  of  a  su- 
pernatural principle. 

It  was  against  this  tendency  that  the  Cartesian 
school  reacted ;  it  rejected  the  hidden  cause  presented 
to  it ;  but  it  rejected,  at  the  same  time,  both  the  cause 
and  the  effects  demonstrated  by  experiment.  It  closed 
its  eyes  in  order  not  to  behold  the  new  astronomical 
system,  and  it  obstinately  persisted  in  its  fanciful  sys- 
tem of  physics.  It  fell  into  ridicule,  and  the  hypothe- 
sis of  vortices,  of  which  Fontenello  was  the  last 
defender,  drew  down  in  its  fall  the  whole  Cartesian 
doctrine. 

Thus  one  often  sees,  in  the  conflict  of  human  ideas, 
when  two  great  doctrines  are  violently  opposed  to 
each  other,  one  of  them  succumb  entirely,  and  the 
conquerors  effacing,  without  distinction,  all  that  the 
conquered  had  inscribed  upon  their  banner. 

As  for  us,  who  now  regard  this .  historical  debate 
through  the  softening  influence  of  years,  we  see  the 
ground  upon  which  the  two  hostile  doctrines  might  be 
reconciled.  The  gravitation  of  Newton,*  and  all  the 
facts  which  it  embraces,  appear  to  us  in  harmony  with 
the  Cartesian  principle,  as  consequences  of  the  mo- 
tions of  matter. 


1 86       UNITY  OF  NATURAL  PHENOMENA. 


IV. 


Hypotheses  in  regard  to  the  Formation  of  Worlds  and 
the  Origin  of  Gravity. 

THE  Newtonian  principle  and  the  Cartesian  princi- 
ple, so  long  hostile,  became  united,  and  merged  into 
each  other,  in  the  general  idea  we  are  now  able  to  form 
concerning  the  system  of  the  universe. 

This  general  idea  is  formed  in  our  minds  when  we 
comprise  in  one  general  view  the  hypothesis  of  La- 
place, concerning  the  birth  of  the  solar  system  ;  the 
conjectures  drawn  by  contemporaneous  astronomy, 
from  the  appearance  of  the  nebulae,  and  the  facts  we 
have  developed  above  with  regard  to  the  function  of 
an  ethereal  substance. 

Let  us  begin  by  recounting,  in  a  few  words,  the 
hypothesis  of  Laplace. 

Our  planetary  system  was  at  first  only  a  nebula ;  its 
limits  extended  far  beyond  the  present  orbits  of  our 
planets,  and  ,it  became  successively  condensed  in  the 
course  of  ages. 

Laplace  sketches,  in  grand  outline,  the  history  of 
this  gradual  condensation.  A  solar  nucleus  first 
forms  in  the  nebula.  This  nascent  sun  is  a  gaseous 
mass,  endowed  with  a  motion  of  rotation,  which  it 


THE  ATTRACTIVE  FORCES.          l8/ 

*4 

shares  with  an  immense  atmosphere.  By  the  general 
cooling  of  the  system  this  atmosphere  leaves  suc- 
cessively, in  the  plane  of  its  equator,  lenticular  zones, 
from  which  spring  the  planets.  Sometimes  these 
zones  preserve  the  circular  form,  of  which  the  rings 
of  Saturn  afford  us  examples.  "Most  frequently  they 
separate  into  several  parts.  The  fragments  may  re- 
main ununited,  as  we  observe  in  the  system  of  minor 
planets,  situated  between  Mars  and  Jupiter.  They 
may  also  —  and  this  is  oftenest  the  case  —  be  united 
•together  into  a  single  mass. 

The  planets  thus  formed,  are  originally  gaseous 
masses,  which  continue  to  turn  about  the  sun ;  they 
turn  also  upon  themselves,  because,  in  the  original 
ring,  the  molecules  farthest  removed  from  the  solar 
centre  had  a  greater  velocity  than  the  rest.  By  this 
rotation  each  of  them  takes  the  form  of  a  spheroid, 
flattened  at  the  poles,  and  very  soon,  in  these  minia- 
ture worlds,  is  begun  anew  the  phenomenon  just  now 
explained.  The*  planetary  atmosphere  gives  off  rings, 
from  which  spring  the  satellites. 

The  nuclei  of  the  planets  and  those  of  the  satellites 
become  hard  at  the  surface,  the  atmospheres  become 
denser  between  the  nuclei,  and  the  immense  expanse, 
which  was  first  filled  by  the  nebula,  is  no  longer  occu- 


1 88       UNITY  OF  NATURAL  PHENOMENA. 

pied,  save  by  a  few  celestial  globes,  which  move  regu- 
larly around  their  common  centre. 

The  author  of  the  Mechanique  Celeste  has  only  put 
forth  this  pretentious  hypothesis  with  reserve ;  he 
has  modestly  placed  it  in  a  note  at  the  end  of  his  Ex- 
position of  the  System  of  the  Universe.  It  has  not 
failed  to  assume  a  high  importance,  for  it  is  the  only 
conception  which  accounts  for  the  principal  planetary 
phenomena.  It  explains  why  all  the  planets  circulate 
about  the  sun  almost  in  the  same  plane ;  why  this 
plane  of  general  circulation  is  exactly  that  of  the  solar 
equator ;  why  the  planets  describe  ellipses  which  near- 
ly resemble  circles  ;  why  their  motions  of  progression 
and  of  rotation  take  place  in  the  same  direction  ;  why 
all  the  circumstances  observed  in  the  journey  of  the 
planets  around  the  sun  are  reproduced  in  the  circula- 
tion of  the  satellites  around  their  planets.* 

*  Is  there  need  of  recalling  here  the  brilliant  experiment  to 
•which  a  Belgian  physicist,  M.  Plateau,  has  attached  his  name,  and 
which  reproduces  the  principal  phases  of  thtse  creations  of  the 
heavenly  bodies?  In  a  vase  there  is  placed  a  mixture  of  water 
and  of  alcohol,  in  the  centre  of  which  is  put  a  drop  of  oil.  Into 
this  drop  is  introduced  a  needle,  to  which  a  regular  motion  of  ro- 
tation is  imparted.  The  oily  sphere  turns  on  its  axis,  and  be- 
comes flattened  at  the  poles.  Soon,  from  the  expanded  equation- 
al  regions,  if  the  experiment  is  well  conducted,  there  escapes  a 
sort  of  ring,  which  breaks  into  globules,  each  of  which  begins 
to  turn  about  the  central  mass.  One  may  thus  construct  a  uni- 


THE   ATTRACTIVE   FORCES.  189 

•  4 

The  hypothesis  of  Laplace  leads  us,  then,  from  the 
origin  of  the  sun  to  the  complete  development  of  our 
solar  system ;  but  let  us  now  conceive  of  a  phase 
anterior  to  this,  and  attempt  to  portray  its  history. 

Let  us  go  back  to  a  period,  in  the  succession  of 
ages,  when  no  system  as  yet  existed. 

The  ether  alone  filled  all  space  with  its  atoms  in 
motion. 

If  this  medium  is  strictly  homogeneous  in  all  its 
parts,  a  uniform  vibration  will  continue  without  end ; 
but  if,  among  these  primitive  atoms,  there  exists,  at 
certain  points,  some  dissimilarity,  the  preponderating 
atoms  immediately  become  centres  of  aggregation. 
They  approach  each  other  in  the  manner  we  have  de- 
scribed. A  sort  of  selection  is  thus  effected  through- 
out the  universal  mass ;  the  ether  becomes  more  and 
more  homogeneous  in  proportion  as  the  dissimilar  ele- 
ments become  united  at  certain  centres.  Thus,  there 
is  formed  in  the  midst  of  the  ether,  now  become  more 

verse  in  a  glass  of  water.  The  reader  will  observe,  on  a  little 
reflection,  that  this  experiment  is  not  a  fair  illustration  of  La- 
place's theory.  The  oily  ring  is  thrown  off  by  the  centrifugal 
force  of  the  revolving  globule,  while  in  the  nebular  hypothesis 
the  rings,  out  of  which  the  planets  are  formed,  are  successively 
abandoned  by  the  cooling  and  contraction  of  the  nebular  mass.  — 
Translator. 


IQO       UNITY  OF  NATURAL  PHENOMENA. 

and  more  purified,  a  cosmical  essence  universally  ex- 
tended, the  subtle  germ  of  ponderable  matter. 

It  is,  in  fact,  gravity  that  has  just  taken  its  origin  in 
the  phenomenon  we  have  sketched,  and  it  becomes 
more  clearly  pronounced  in  proportion  as  the  molecu- 
lar groups  are  better  defined,  and  the  ether  reduced  to 
a  state  of  atomic  uniformity. 

Here,  then,  is  space  occupied  by  a  sort  of  embryonic 
network,  the  interstices  of  which  are  filled  by  the 
ethereal  atoms.  The  motion  of  attraction  thus  begun 
never  ceases. 

At  the  same  time  that  the  ether  was  tending  towards 
a  uniform  condition,  the  rudimentary  molecules  were 
absorbing  all  the  unlike  elements  ;  thus  they  have 
been  unequally  pressed  upon  in  different  directions  ; 
the  motions  of  progression  and  rotation  follow  as  a 
natural  consequence. 

Variety  is  also  characteristic  of  the  cosmical  net- 
work, from  the  very  nature  of  its  origin ;  it  becomes 
torn  then  into  irregular  shreds  here  and  there,  where 
the  effects  of  concentration  are  manifested. 

We  here  reach  a  point  where  telescopic  observation 

comes  to  the  aid  of  pure  speculation.      The  farther 

'   artronomers  penetrate  into  the  depth  of  the  heavens, 

the  greater  is  the   number  of  these  cosmical   bodies 

which  they  discover,  some  of  which  are  resolvable  into 


THE  ATTRACTIVE  FORCES.  IQI 

stars,  while  others  preserve  trie  appearance  of  irredu- 
cible nebulosities.  Do  these  latter  owe  this  appear- 
ance to  distance  only  ?  and  are  we  to  believe  that  by 
the  aid  of  stronger  lenses  they  could  be  decomposed 
into  luminous  points  ?  Opinion  may  vary  in  regard  to 
this  in  such  or  such  particular  case,  with  reference  to 
such  or  such  especial  nebula  ;  but  the  aggregate  of 
observations  leads  to  the  belief  that  these  agglomera- 
tions are  worlds  in  various  stages  of  formation.  In 
some,  the  cosmical  matter  would  be  still  diffused  ;  in 
others,  the  solar  nuclei  would  be  more  or  less  formed  ; 
in  others,  again,  the  suns  would  have  already  generated 
their  corteges  of  satellites. 

Thus  we  should  have  before  us,  more  or  less  accessi- 
ble to  our  telescopes,  specimens  of  the  various  phases 
through  which  worlds  pass. 

Greater  importance  will  not  attach  to  these  sugges- 
tions than  they  deserve.  If  Laplace  deferred  his  hy- 
pothesis to  the  end  of  one  of  his  books,  where  shall  we 
assign  the  place  of  the  cosmical  outline  just  sketched  ? 
We  have  attempted  to  carry  back  to  the  very  origin  of 
cosmical  formations  that  conception  which  represents 
to  us  gravity  as  a  consequence  of  the  motions  of  ether. 
The  views  we  have  given  in  this  connection  may  seem 
unjustifiable.  They  may  be  rejected  without  at  the 
same  time  weakening  the  considerations  which  bear 


UNITY  OF  NATURAL  PHENOMENA. 

upon  the  nature  itself  of  gravity,  such  as  we  can 
observe  it  to  be  in  our  own  world,  in  the  midst  of 
circumstances  accessible  to  our  analysis. 


V. 

The  Molecular  Agencies,  Cohesion,  and  Chemical 
Affinity. 

WE  must  now  return,  by  an  abrupt  transition,  from 
the  motions  of 'heavenly  bodies  to  the  molecular  phe- 
nomena ;  from  the  immense  spaces  to  which  gravity 
extends  to  the  infinitely  small  distances  in  which  co- 
hesion and  chemical  affinity  display  themselves^  We 
have  already  pointed  out  the  enormous  power  of  these 
last  two  forces  ;  but  the  numerical  results  we  have 
mentioned  give  only  a  faint  idea  of  it.  It  is  known 
that  changes  in  cohesion,  the  freezing  of  water,  for 
example,  and  the  solidifying  of  bismuth,  may  shatter 
iron  bottles  of  the  thickness  of  several  centimeters  ; 
we  say  nothing  of  the  formidable  effects  produced  by 
the  action  of  affinities  in  explosible  mixtures  ;  the 
simple  reactions  which  form  and  maintain  the  ordinary 
aggregations  of  matter  have  a  power  so  great  that 
they  have  been  called,  in  figurative  language,  giants  in 
disguise. 


THE  ATTRACTIVE  FORCES.  193 

i 

It  seems  at  first  thought  that  the  heavenly  bodies,  in 
their  journey  through  space,  must  use  up  the  largest 
part  of  the  vis  viva,  or  living  force,  diffused  throughout 
the  universe  ;  the  contrary  is  true.  The  living  force, 
represented  by  the  motions  of  the  heavenly  bodies,  is 
very  weak  compared  with  that  concentrated  in  the 
molecular  activities. 

Before  making  a  new  step  in  the  examination  of 
these  activities,  it  is  important  that  we  recur  to  the 
idea  itself  of  the  molecule,  and  that  we  define  its 
meaning.  The  molecules  of  bodies  reputed  to  be  sim- 
ple, such  as  oxygen,  hydrogen,  carbon,  are  they  indi- 
visible unities,  veritable  atoms,  or  are  they  aggrega- 
tions ? 

This  latter  hypothesis,  we  have  already  said,  alone 
seems  admissible. 

After  the  first  labors  which  established  the  science 
of  chemistry,  when  analysis  stopped  before  a  certain 
number  of  substances  which  it  could  not  decompose, 
one  was  led  to  look  upon  these  substances  as  different 
in  their  very  nature.  Such  was  the  doctrine  of  Ber- 
gelius.  By  this  theory  carbon,  gold,  and  platinum  are 
bodies  entirely  heterogeneous,  their  atoms  enjoying 
special  and  peculiar  properties.  Nevertheless,  the 
notion  of  equivalents,  introduced  into  chemistry  at 
the  beginning  of  this  century,  naturally  inclined  men's 
13 


194        UNITY  OF  NATURAL  PHENOMENA. 

minds  towards  a  different  doctrine.  When  it  was  seen 
that  simple  bodies  combine  and  replace  each  other  in 
their  combinations  in  clearly  defined  proportions,  the 
equivalent  quantities  of  different  bodies  came  necessa- 
rily to  be  regarded  as  different  collections  formed  out 
of  one  and  the  same  substance. 

Prout  was  the  first  to  give  definite  shape  to  this 
opinion.  According  to  him,  the  equivalent  weights  of 
simple  bodies  were  the  multiples  of  that  of  hydrogen. 
It  was  very  soon  observed  that  this  law  could  not  be 
maintained  in  the  exact  terms  of  its  annunciation. 
The  precise  determination  of  certain  equivalents  was 
not  in  agreement  with  it.  The  first  exceptions  were 
made  to  disappear  by  taking  as  unity  the  half  equiva- 
lent of  hydrogen  ;  but  new  difficulties  arose,  and  it 
was  necessary  to  have  recouise  to  a  more  complicated 
division.  Front's  law  has  thus  lost,  little  by  little,  its 
primitive  originality.  It  remains,  notwithstanding, 
corrected  by  necessary  restrictions,  as  an  important 
agreement  in  favor  of  the  elementary  unity  of  bodies. 

We  have  already  shown  how  the  new  physics  goes 
back  to  the  very  ethereal  atoms  for  this  elementary 
unity.  Between  the  molecules  of  oxygen,  of  hydrogen, 
of  carbon,  of  gold,  of  platinum,  it  conceives  of  no  dif- 
ference which  bears  upon  the  quality  of  matter  ;  it  be- 
holds only  in  these  different  bodies  the  properties 


THE   ATTRACTIVE   FORCES.  1 95 

*• 

which  result  from  motion.  If  this  is  true  of  these 
bodies  compared  with  each  other,  it  is  true  also  of  the 
same  bodies  compared  with  the  ether.  Between  them 
and  the  ether  where  could  there  be  found  a  difference 
which  should  have  an  influence  upon  their  material 
quality  ?  Thus  every  elementary  molecule  appears  to 
us  as  formed  of  ethereal  atoms.  Heat  disorganizes 
bodies  ;  it  goes  so  far  as  to  separate  the  hydrogen  and 
the  oxygen,  which  form  the  vapor  of  water  ;  there 
would  be  a  final  step  to  make ;  by  additionally  heating 
these  same  molecules,  they  might,  doubtless,  in  the 
end  be  driven  apart,  and  be  resolved  into  ethereal 
atoms,  either  directly  or  by  successive  steps. 

Here,  then,  is  the  manner  in  which  the  scale  of 
material  aggregation  presents  itself  to  our  eyes.  In 
the  state  of  extreme  tenuity,  the  ethereal  atom  ;  then 
comes  the  elementary  molecule  of  bodies  regarded  as 
simple  ;  these  molecules  combine,  and  from  them  re- 
sult compound  or  chemical  molecules.  These  last 
unite  in  their  turn,  and  thus  form  the  particles  of 
bodies. 

It  may  be  conceived,  at  least  in  a  general  way,  how 
the  aggregation  of  an  elementary  molecule  may  result 
from  the  activity  of  a  medium  and  the  relative  motions 
of  its  parts.  Without  insisting  upon  this  point,  we 
can  represent  this  order  of  phenomena  by  means  of 


UNITY    OF   NATURAL   PHENOMENA. 

several  rough  examples,  a  few  far-fetched  analogies. 
It  is  in  this  manner  that  the  pressure  of  the  air  main- 
tains, in  opposition  to  each  other,  the  segments  of  a 
hollow  sphere.  It  is  thus  that  a  liquid  jet  often  as- 
sumes the  appearance  and  the  consistency  of  a  solid 
through  the  common  motion  of  its  parts.  It  is  thus 
that  we  often  see  eddies  of  wind  or  of  dust  pass  over 
long  distances  without  losing  their  shape,  because  the 
elements  that  compose  them  are  endowed  with  the 
same  angular  velocity. 

It  is  equally  true,  if  one  examines  these  questions 
closely,  that  the  new  physics,  in  the  light  it  throws 
upon  them,  only  reveals  to  us  a  few  fugitive  outlines. 
We  should  demand  of  it  in  vain  to  show  by  some 
decisive  examples  how  the  various  properties  of  mole- 
cules arise  from  a  combination  of  motions.  This 
diversity,  which  springs,  so  to  speak,  from  the  very 
bosom  of  matter,  always  has  been,  and  still  remains 
one  of  the  strangest  phenomena  which  man  can 
investigate. 

Early  science  saw  in  bodies  a  kind  of  duality ;  it 
imagined,  on  one  part,  a  matter  deprived  of  qualities 
of  its  own,  but  capable  of  receiving  them  all,  and  on 
the  other  essences,  which  joined  themselves  to  bodies 
in  order  to  constitute  their  properties  ;  it  supposed 
that  these  essences  could  be  isolated  by  distillation, 


THE    ATTRACTIVE    FORCES. 
k 

and  the  alchemist  strove  to  collect  them,  in  order  to 
infuse  them  into  matter  at  his  will. 

After  the  doctrine  of  essences,  there  prevailed  the 
idea  of  forms  ;  an  aesthetic  principle,  concealed  in  the 
interior  of  bodies,  determined  the  moulds  in  which  the 
molecular  diversity  was  produced.  Let  us  remark 
that  this  conception  approaches  that  of  motion.  The 
idea  of  motion  does  not  ultimate  itself  without  a  cer- 
tain idea  of  form  ;  geometry  determines  the  curves, 
and  the  ideal  surfaces  in  which  the  motions  are  pro- 
duced, and  by  which  they  are  limited. 

The  new  physics  refers  to  motion  the  structure  and 
properties  of  molecules.  It  draws  this  conclusion  from 
the  aggregate  of  laws  which  it  has  discovered  ;  it 
believes  itself  authorized  in  this  by  what  it  knows 
of  several  great  natural  phenomena  ;  by  what  it  has 
learned  of  light,  heat,  and  electricity  ;  by  the  induc- 
tions to  which  it  has  been  brought  regarding  the  na- 
ture of  universal  attraction.  But  the  future  alone  will 
show  whether  it  can  reach  the  original  conditions 
which  diversify  the  motions  taking  place  in  the  hidden 
depths  of  matter. 

We  must  not  occupy  ourselves  longer  with  the 
metaphysics  of  molecules.  The  principal  results  we 
have  successively  enunciated  are  independent  of  every 
hypothesis  concerning  the  constitution  of  molecules. 


UNITY  OF  NATURAL  PHENOMENA. 

We  have  been  careful  to  reserve  the  term  Atom  for 
the  elements  of  the  ether,  and  to  apply  the  name  of 
molecule  to  those  of  ponderable  matter  ;  but  other- 
wise, throughout  the  course  of  this  work,  if  certain 
incidental  theories,  which  are  easily  separated  from  it, 
be  put  aside,  we  may  preserve  the  primitive  notion 
furnished  by  chemistry,  and  regard  the  elementary 
molecules  as  little  indivisible  blocks,  whose  interior 
construction  possesses  no  influence  over  phenomena. 

It  has  been  seen  how  molecules,  immersed  in  ether, 
come  to  attract  each  other.  We  require  a  new  princi- 
ple to  explain  cohesion,  and  we  find  it  in  the  hypothe- 
sis of  molecular  rotation,  from  which  Father  Secchi 
has  drawn  so  many  ingenious  results. 

In  their  rotation  molecules  must  carry  along  with 
them  an  atmosphere  of  ethereal  atoms  ;  this  is  a  fact 
we  have  already  made  prominent  when  treating  of  the 
change  of  state  of  bodies.  The  existence  of  these 
atmospheres  —  and  here  we  must  avoid  a  possible 
confusion  —  is  entirely  distinct  from  the  phenomenon 
which  distributes  the  ether  in  layers  of  different  den- 
sity. This  latter  effect  extends  to  infinity ;  the  former 
takes  place  only  in  a  very  limited  space,  in  the  imme- 
diate vicinity  of  the  molecule.  In  this  space  the  atoms 
share  directly  in  the  molecular  rotation  ;  outside  of 
it  they  are  independent  of  it.  It  has  been  shown 


THE   ATTRACTIVE   FORCES.  1 99 

above  how  these  atmospheres  behave  when  a  body, 
losing  its  heat,  is  brought  from  the  gaseous  state  to  the 
liquid  form,  and  from  this  to  the  solid  condition.  Let 
us  remark  here,  that  this  hypothesis  explains  why  the 
liquid  and  solid  states  take  place  all  at  once,  at  a  given 
moment,  when  the  molecules  have  been  brought  within 
a  fixed  distance  of  each  other.  So  long  as  the  atmos- 
pheres do  not  touch,  no  trace  of  cohesion  shows  itself ; 
when  they  meet,  this  force  arises.  We  understand 
also  why  the  temperatures  of  melting  and  solidifying 
are  fixed  for  the  same  body ;  these  effects  take  place 
at  the  precise  moment  when  the  atmospheres,  varying 
with  the  temperature,  have  attained  the  desired 
diameter. 

Now  what  is  affinity  ?  Let  us  note  the  nature  of 
its  action.  It  acts  for  a  time,  more  or  less  precipitate- 
ly, in  order  to  disturb  an  equilibrium  ;  the  bodies  con- 
cerned saturate  each  other  ;  then  a  new  equilibrium 
succeeds.  This  phenomenon  may  be  explained  by  the 
very  hypothesis  we  have  just  made  use  of. 

Between  homogeneous  molecules  all  the  atmos- 
pheres are  alike,  and  there  is  no  cause  determining 
one  to  modify  the  other.  In  this  case  cohesion  is 
produced.  If,  on  the  other  hand,  molecules  of  differ- 
ent kinds  confront  each  other,  there  is  a  variety  in  the 
atmospheres  ;  these  may  penetrate  each  other,  and 


2OO       UNITY  OF  NATURAL  PHENOMENA. 

modify  in  this  way  the  position  of  their  respective 
molecules. 

In  this  way  the  principle  of  chemical  affinity  be- 
comes known  to  us. 

The  more  unequal  are  the  atmospheres,  the  more 
opportunity  will  there  be  for  the  equilibrium  to  be 
destroyed,  and  the  greater  will  be  the  energy  of  the 
chemical  action.  They  may  differ,  besides,  not  only 
in  their  volume,  but  also  in  their  velocities,  and  they 
thus  present  several  elements  of  variation.  Tempera- 
ture naturally  influences  the  state  of  the  atmospheres, 
and  thereby  changes  the  conditions  of  affinity.  It 
may  happen  that  two  molecules,  which  have  at  a  cer- 
tain moment  dissimilar  atmospheres,  and  consequently 
a  very  great  affinity,  shall  come  to  have,  if  the  temper- 
ature changes,  like  atmospheres,  and  consequently  a 
moderate  affinity.  It  may  even  result,  if  the  tempera- 
ture continues  to  vary,  that  the  relative  value  of  the 
atmospheres  will  be  reversed.  Known  anomalies 
could  thus  be  accounted  for  ;  in  this  manner  could 
be  explained  why,  at  temperatures  very  near  each 
other,  we  sometimes  see  iron  decomposing  water,  and 
setting  the  hydrogen  at  liberty  ;  and  sometimes,  on 
the  contrary,  the  hydrogen  decomposing  the  oxide  of 
iron  in  order  to  get  possession  of  the  oxygen. 


THE  ATTRACTIVE  FORCES.  2OI 

The  chemical  molecule  has  then  a  general  envelope, 
but  that  is  not  to  say  that  the  elementary  molecules 
remain  without  their  own  minor  atmospheres.  It 
must  be  observed,  moreover,  that  these  general  atmos- 
pheres are,  so  to  speak,  external  phenomena,  in  which 
we  naturally  find  again  the  motions  themselves  of  the 
molecules.  Between  all  these  motions,  those  of  the 
molecules,  those  of  the  partial  envelope,  and  those  of 
the  general  envelope,  an  equilibrium  is  established, 
from  which  results  the  stability  of  the  combination. 
The  compound  will  be  so  much  the  more  stable  as 
this  dynamic  equilibrium  shall  have  less  chance  of 
being  disturbed.  If  the  elements  are  numerous,  a 
slight  variation  of  temperature  puts  disorder  into  this 
aggregation,  and  destroys  its  bonds  of  union. 

This  effect  shows  itself  more  clearly  in  proportion 
as  we  go  from  the  mineral  kingdom,  where  a  certain 
simplicity  reigns,  to  organic  substances,  the  structure 
of  which  is  more  complicated.  It  is  said  that  a  mole- 
cule of  albumen  contains  nine  hundred  elementary 
molecules.  It  is  conceivable  that  compounds  so  com- 
plex may  be  easily  destroyed  by  variations  of  tempera- 
ture. The  complication  is  much  greater  yet  in  organ- 
ized tissues.  Thus  vegetables  are  confined  each  to  a 
particular  climate,  and  if  animals  are  able  to  live  in 
regions  more  extended,  it  is  because  they  carry  in 


2O2        UNITY  OF  NATURAL  PHENOMENA. 

themselves  a  source  of  heat  which  renders  the  tem- 
perature of  each  almost  constant. 

From  the  time  of  Lavoisier,  the  science  of  chemis- 
try has  been  constructed  upon  the  idea  of  masses ; 
its  relation  to  velocities  remains  wholly  to  be  estab- 
lished. Now  masses  and  velocities  form  two  series 
of  elements,  which  it  is  equally  necessary  to  be  ac- 
quainted with  in  order  to  appreciate  the  living  forces 
with  which  molecules  are  endowed,  and  the  varying 
results  which  they  may  thus  give  rise  to. 
•  We  cannot  refrain  from  remarking,  however,  that 
chemistry  has  made  universal  progress  through  the 
consideration  of  masses  only.  The  law  of  definite 
proportions,  the  law  of  multiple  proportions,  even  the 
notion  of  chemical  equivalence,  which  naturally  re- 
sulted from  these  two  fundamental  laws,  are  indepen- 
dent of  all  idea  of  motion.  By  means  of  their  rela- 
tive weights  simple  bodies  have  been  followed  into 
their  elementary  combinations,  and  the  scale  of  their 
saturation  determined.  Later,  organic  chemistry  be- 
comes founded,  through  the  study  primarily  of  fatty 
substances,  afterwards  through  the  first  analyses  of 
the  alcohols  and  ethers  ;  the  scales  then  prove  insuffi- 
cient for  pursuing  the  complication  of  phenomena,  and 
yet  the  theories  which  chemistry  gives  rise  to  seem, 
at  first  sight,  to  be  applicable  only  to  molecules  in  a 


THE  ATTRACTIVE  FORCES.          2O3 

state  of  repose.  The  law  of  substitutions  sums  up 
the  progress  of  organic  chemistry.  This  law  does  not 
imply,  so  at  least  one  might  think,  any  idea  of  molec- 
ular motion  ;  it  may  be  understood  as  the  mutual 
replacement  of  partial  groups  among  motionless  groups 
of  atoms,  if  one  is  satisfied  with  a  summary  view  of  it. 
But  we  no  longer  need  show  what  incompleteness  such 
a  manner  of  appreciating  chemical  phenomena  would 
possess.  It  would  not  be  possible  to  compare  molec- 
ular structure  to  the  superposition  of  the  stones  of  a 
building  ;  if  it  is  to  be  represented  by  an  appropriate 
figure,  we  must  liken  it,  on  a  limited  scale,  to  solar  vor- 
tices which  should  penetrate  each  other,  and  whose 
elements  should  take  on  in  the  encounter  a  new  and 
unstable  equilibrium. 

Furthermore,  we  are  not  here  dealing  with  a  merely 
theoretical  conception.  If  we  return  to  the  domain  of 
facts,  we  see  that  chemical  action  produces  a  work,  a 
result  peculiar  to  masses,  endowed  with  velocity.  It 
is  chemical  action  ;  it  is  the  combustion  of  coal  that 
sets  the  most  of  our  engines  in  motion. 

Just  now  we  do  not  know  how  to  make  a  direct 
i 

measurement  of  chemical  work ;  we  determine  it  only 
through  the  medium  of  heat  or  of  electricity  ;  by  these 
indirect  means  we  already  obtain  an  appreciation  of  it 
sufficiently  exact.  We  judge  of  chemical  action  by  its 


204       UNITY  OF  NATURAL  PHENOMENA. 

exterior  effects,  and  it  is  a  result  not  to  be  despised. 
To  know  it  in  itself,  to  penetrate  its  secret,  to  com- 
prehend its  interior  play,  we  must  determine  the 
velocities  as  well  as  the  molecular  masses.  If  we  were 
in  possession  of  the  terms  of  this  twofold  quality,  we 
should  see  disappear  all  that  chemistry  yet  retains  that 
is  whimsical  and  capricious  ;  we  might  explain  the  dif- 
ferent combinations,  and  the  material  properties  re- 
sulting from  them. 

Then  would  be  established  molecular  mechanics, 
which  would  comprehend  in  their  entirety,  not  only 
chemical  phenomena,  but  all  the  natural  phenomena 
we  have  successively  treated  of,  those  of  gravity  as  well 
as  those  of  heat,  those  of  electricity  as  well  as  those 
of  light ;  a  universal  system  of  dynamics  would  em- 
brace astronomy,  physics,  and  chemistry. 


LIVING   BEINGS.  20$ 


CHAPTER  VI. 

• 

LIVING   BEINGS. 

I. 

Vital  Activity  consists  in  the  Transformation,  not  in 
the  Creation  of  Motions. 

WE  have  nearly  exhausted  the  programme  we  had 
marked  out  in  advance ;  we  have  directed  our  atten- 
tion successively  to  the  principal  phenomena  pertaining 
to  the  physical  sciences  ;  we  have  shown  their  mutual 
relations,  and  pointed  out  their  fundamental  unity. 
We  could  here  terminate  our  examination,  and  con- 
sider our  task  as  accomplished  ;  the  results  we  have 
reached  now  appear  in  their  general  bearing.  We 
have  not  yet,  however,  paid  any  attention  to  living 
beings,  which  also  form  a  part  of  the  physical  uni- 
verse. Should  they  also  be  comprehended  in  the  phe- 
nomenal unity  upon  which  we  have  fixed  our  attention, 
or  should  they  be  excluded  from  it  ?  Do  they  wholly 
obey  the  laws,  whose  mutual  connection  has  been 


2O6       UNITY  OF  NATURAL  PHENOMENA. 

shown,  or,  if  they  are  independent  of  them  in  some 
respects,  what  are  their  immunities  ? 

The  simple  enunciation  of  these  questions  calls  to 
mind  the  vast  problems  that  have,  from  time  to  time, 

agitated  mankind ;  so  many  theories  concerning  the 

• 

nature  of  life,  so  much  effort  laid  out  on  human  per- 
sonality, so  many  discussions  in  regard  to  the  princi- 
ples of  a  higher  essence  !  Let  it  not  be  expected  that 
we  shall  attack  these  lofty  questions.  We  may  re- 
serve them  intact,  and  we  need  not  venture  upon  the 
field  of  transcendental  speculation  in  order  to  show 
how  the  great  law  under  which  we  have  brought 
the  operations  of  nature  is  verified  also  in  organized 
beings. 

It  seems,  according  to  the  labors  of  modern  physi- 
ology, that  in  the  cell  must  be  sought  the  principle  of 
vital  activity.  Vegetables,  like  animals,  are  composed 
of  cells. 

Every  vegetable  is  composed  of  an  association  of  lit- 
tle sacs  or  vesicles  which  assume,  in  crowding  together, 
the  polyhedral  form.  Each  one  forms  a  closed  organ 
which  has  its  own  life,  and  which  is,  as  it  were,  the 
integral  part  of  the  vegetable. 

The  case  is  not  otherwise  with  animals  ;  but  the 
more  perfect  the  general  organism,  the  greater  the 
variety  observable  in  the  cells.  In  the  lower  degrees 


LIVING   BEINGS.  2O/ 

of  the  animal  scale,  among  the  infusoria  of  the  lowest 
species,  are  found  creatures  of  the  simplest  composi- 
tion that  it  is  possible  to  imagine.  The  cells,  all  of 
them,  entirely  similar  to  each  other,  fill  an  envelope 
furnished  with  vibratile  cilia,  by  the  aid  of  which  the 
animal  moves.  With  the  higher  animals,  with  verte- 
brates, with  man,  there  are  great  differences  between 
the  cells  belonging  to  the  tissues  of  different  organs. 
A  nucleus,  more  or  less  complex,  at  the  centre,  a  fine 
membrane  at  the  periphery,  between  the  two  a  liquid, 
either  simple  or  compound,  —  such  are  the  constituent 
principles  of  the  cell,  and  they  exhibit  a  sufficient 
variety  of  elements  to  display  very  great  dissimilarities 
between  the  cells  composing  the  different  muscular 
fibres,  the  various  nervous  filaments,  the  mucous  and 
serous  membranes,  &c.  In  the  midst  of  this  diversity, 
each  cell  possesses,  in  the  interior  of  the  collective 
being,  a  relative  independence,  a  sort  of  autonomy. 
Every  family  of  these  vesicles  has  its  own  govern- 
ment, its  food,  poisons,  diseases. 

Moreover  it  is  known,  since  the  ingenious  discover- 
ies of  Dutrochet,  how  these  little  sacs  are  nourished, 
though  entirely  closed,  separated  even  from  each  other 
by  the  double  partition  which  results  from  their  back 
to  back  arrangement ;  it  is  known  that  they  succeed 
in  absorbing  the  liquids  outside  of  them,  and  in  ex- 


2O8       UNITY  OF  NATURAL  PHENOMENA. 

pelling,  in  part,  those  with  which  they  are  filled.  This 
phenomenon  of  endo-exosmosis,  together  with  capil- 
lary attraction,  is  sufficient  to  account  for  the  ascent 
and  descent  of  the  sap  in  vegetables.  It  shows  how 
in  animals  the  different  cells  may  incessantly  renew 
their  contents,  and  obtain,  by  an  elective  straining  pro- 
cess, all  that  is  needed  for  their  support.  Not  only 
are  these  vesicles  nourished,  thanks  to  this  mechan- 
ism, but,  by  an  action  communicated  from  one  to 
the  other,  they  succeed  in  drawing  up  liquids  through 
canals  that  have  no  opening,  and  in  pouring  them  into 
other  canals  equally  closed,  thus  establishing  through- 
out the  mass  of  the  tissues  a  capillary  circulation,  the 
principle  of  which  for  a  long  time  escaped  all  re- 
search. 

Thus  we  find,  at  the  origin  of  life,  cells  which  form 
the  primary  bases  of  organization.*  It  may  be  said 
that  they  constitute,  in  the  two  organic  kingdoms,  in- 
dividuals that  may  be  compared  with  the  atoms  of  the 
mineral  kingdom  ;  atom,  individual,  two  terms  bor- 

*  Concerning  the  character  of  the  life  of  these  ultimate  cells, 
see  Physical  Basis  of  Life,  T.  H.  Huxley.  The  substance,  pro- 
toplasm, which  is  considered  in  this  treatise  as  forming  the 
structural  unit  of  all  vegetable  and  animal  life, 'contains  only  the 
four  elements,  carbon,  oxygen,  hydrogen,  and  nitrogen.  —  Trans- 
lator. 


LIVING   BEINGS.  2OQ 

rowed  from  different  languages  to  express  the  same 
idea. 

But  do  we  know  how  the  cells  are  produced  ?  and 
has  the  secret  of  their  formation  been  discovered  ? 
We  have  seen  in  the  germ  of  vegetables  a  primary 
cell  nourished  by  the  starch  contained  in  the  grain, 
and  converted  by  the  process  of  germination  into  dex- 
trine and  sugar ;  we  have  seen  new  cells  arrange  them- 
selves beside  the  first  one  by  a  process  of  germination 
or  budding  ;  the  soluble  substances,  elaborated  in  this 
rudimentary  life,  thus  come  to  constitute  the  primary 
elements  of  vegetables.  In  the  animal  germ,  in  the 
egg,  we  see  a  granular  matter  dividing  itself  into  sev- 
eral spheroidal  segments,  and  each  of  these  converted 
into  a  vesicle  by  the  coagulation  of  its  superficial 
layer ;  then  the  vesicles  attach  themselves  to  each 
other,  multiply  themselves  by  division  by  the  forma- 
tion of  interior  membranes,  and  finally  constitute  the 
cellular  tissue,  out  of  which  is  to  come  the  embryo. 
It  is  in  this  tissue  that  are  arranged,  by  an  analogous 
mechanism,  the  rudiments  of  organs,  of  a  circulatory 
apparatus,  and  a  nervous  system. 

As  to  the  elements  themselves  which  compose  liv- 
ing organisms,  vegetable  or  animal,  it  is  here  unneces- 
sary to  recall  the  fact  that  they  are  all  borrowed  in 
their  last  analysis  from  the  inorganic  world.  As  we 
14 


2IO       UNITY  OF  NATURAL  PHENOMENA. 

ascend  the  animal  scale,  we  find  an  increasing  compli- 
cation in  this  respect,  notwithstanding  there  never 
enters  into  living  beings  more  than  a  very  limited 
number  of  simple  bodies.  The  human  body,  the  most 
complex  of  all,  comprises  fourteen  simple  bodies  — 
oxygen,  hydrogen,  azote,  carbon,  sulphur,  phosphorus, 
fluorine,  chlorine,  sodium,  potassium,  calcium,  magne- 
sium, silicon,  and  iron.  However  complicated  may  be 
the  architecture  of  the  molecules,  the  entire  man  is 
reducible  to  these  fourteen  elements. 

If  we  now  attempt  to  condense  the  primordial  no- 
tion of  life,  such  as  it  results  from  these  suggestions, 
if  we  strive  to  reduce  it  to  its  essential  principles, 
what  do  we  find  ? 

On  the  one  side,  the  materials  themselves  of  the  in- 
organic world. 

On  the  other  side,  a  series  of  motions,  which  suc- 
ceed each  other  in  a  determined  order. 

The  definite  succession  of  these  motions  doubtless 
exhibits  a  character  entirely  unique,  but  throughout 
their  successive  transformations  there  will  be  found 
nothing  in  them  which  jars  with  the  laws  of  molecular 
mechanics.  • 

Do  we  mean  that  we  have  here  all  the  elements  of 
life  ?  What  is  the  cause  which  forms  the  first  cellule, 
which  produces  from  it  the  development  of  the  being, 


LIVING   BEINGS.  211 

which  regulates  and  limits  its  evolution  ?  In-  view 
of  the  facts,  it  is  too  evident  that  we  cannot  reply  to 
this  question.  We  have,  then,  only  two  courses  to 
pursue  —  either  to  suspend  our  judgment,  or  to  admit 
a  special  cause,  the  principle  of  which  is  peculiar  to 
vital  phenomena. 

With  the  nature  itself  of  this  course  we  have  not 
to  concern  ourselves  here ;  and,  since  it  is  manifested 
by  means  of  motions,  its  name  is  to  be  found  in  the 
language  we  speak,  we  must  call  it  a  force. 

What  do  the  preliminary  considerations  we  have 
just  laid  down  teach  us  concerning  the  action  of  this 
force  ?  Upon  this  point  there  must  be  a  thorough 
understanding.  It  determines  motions,  but  it  can  only 
produce  them  at  the  expense  of  anterior  motions  ;  just 
as  it  does  not  create  the  materials  of  organisms,  but 
merely  shapes  them  by  the  aid  of  pre-existing  elements, 
so  it  does  not  create  motions,  but  only  transforms 
them.  It  is  thus  that  vital  phenomena,  without  losing 
their  special  character,  enter  entirely  into  the  cate- 
gory of  material  motions.  If  the  vital  force  has  a 
peculiar  activity,  this  activity  consists  in  transforming, 
not  in  creating.  It  furnishes  us,  then,  with*  a  fresh 
confirmation  of  the  great  law  whose  development  we 
are  seeking  throughout  the  entire  universe. 


212       UNITY  OF  NATURAL  PHENOMENA. 

Such  is  the  stand-point  to  which  we  shall  constant- 
ly be  brought  whenever  we  consider  the  phenomena 
of  life  * 

*  The  tendency  of  modern  science  is  to  include  in  the  same 
category  all  displays  of  force,  whether  exhibited  in  organized 
beings  or  inorganic  things.  Heat,  light,  chemical  affinity  and 
vitality  are  thus  mutually  correlated.  The  idea  of  a  distinct 
principle  of  vitality  is,  however,  openly  claimed  by  many,  and 
tacitly  acknowledged  by  most  scientific  writers  of  the  present 
day.  But  the  old  boundary  lines  between  the  animal  and  vegeta- 
ble kingdoms  it  has  been  necessary  to  abandon,  since  the  micro- 
scope has  disclosed  by  its  keen  scrutiny  that  no  such  lines  exist. 
Even  the  power  of  voluntary  motion,  supposed  to  be  the  exclusive 
privilege  of  animals,  has  its  analogies,  if  not  its  exact  counter- 
part, in  the  spontaneous  movements  of  many  species  of  plants. 
The  distinction  between  the  mineral  kingdom  and  the  other  two, 
between  the  inanimate  on  the  one  hand  and  the  animate  on  the 
other,  is  equally  ill-founded,  for  the  truth  seems  to  be  that  all 
created  things  possess  life,  each  in  the  degree  and  kind  corre- 
sponding to  its  use*  and  destiny  in  the  order  of  creation.  Like- 
wise the  subdivisions  of  these  kingdoms,  with  their  systems  of 
classification,  prove  but  temporary  make-shifts,  which  need  to  be 
constantly  modified.  The  real  fundamental  distinctions  which 
undoubtedly  exist  between  the  three  kingdoms  of  nature,  appear 
unattainable  by  science,  whose  province  is  to  deal  with  effects, 
and  not  with  causes.  Our  author  has  thought  best  not  to  touch 
upon  these  vexed  questions ;  but  we  must  admit  that  his  asser- 
tion that  vital  phenomena,  as  being  but  manifestations  in  matter 
of  an  interior  active  principle,  can  be  included  in  the  category 
of  material  motions,  is  fully  sustained  by  the  results  of  modern 
investigation.  —  Translator. 


LIVING   BEINGS. 


II. 

The  Manner  in  which  the  Laws  of  Thermo-dynamics 
are   Verified  in  the  Case  of  Animated  Beings. 

THE  respiration  of  animals,  the  circulation  of  the 
blood,  nutrition,  all  contribute  to  a  production  of  heat. 
A  production  of  heat  is  the  grand  result  of  all  these 
functions.  Now  direct  observation  has  succeeded  in 
tracing  this  into  its  essential  conditions,  and  in  show- 
ing how  the  heat  is  produced  in  accordance  with  the 
principles  of  Thermo-dynamics. 

First,  let  us  regard  the-  state  of  repose  ;  let  us  con- 
sider the  condition  of  a  man  who  performs  no  external 
work. 

Animal  heat  results  from  the  slow  oxidations  which 
take  place  within  the  organism.  It  may  be  added  that 
it  is  due  almost  entirely  to  the  combinations  of  oxygen 
with  hydrogen  and  carbon.  It  is  easy,  then,  by  com- 
paring the  gases  which  enter  and  come  from  the  lungs, 
to  calculate  the  number  of  heat-units  which  a  man 
produces  in  an  hour.  This  is  found  to  be  an  average 
of  one  hundred  and  twenty  heat-units,  with  a  varia- 
tion, according  to  the  subject,  of  about  a  third  of  this 
total  amount. 

What  becomes  of  the  heat-units  thus   produced  ? 


214       UNITY  OF  NATURAL  PHENOMENA. 

The  man  must  necessarily  lose  them  as  fast  as  devel- 
oped, since  the  temperature  of  his  body  remains  con- 
stant.* He  gives  it  forth,  in  fact,  under  several  forms, 
—  pulmonary  and  cutaneous  evaporation,  heating  of 
the  expired  air,  radiation,  contact  with  external  objects. 
If  the  amount  of  heat  emitted  from  the  body  in  these 
various  ways  be  directly  measured,  it  will  be  found  fo 
equal  that  which  is  produced  within  the  body  ;  and  so 
observation  confirms  the  preconceptions  of  the  theory. 
Let  us  observe  that,  in  the  loss  to  be  established 
between  man  and  the  surrounding  medium,  we  have 
not  reckoned  the  work  which  is  accomplished  in  the 
interior  of  the  body.  The  heart,  for  example,  operates 
constantly  after  the  manner  of  a  force-pump  ;  it  acts 
incessantly  with  a  force  that  may  be  estimated  at  the 
seventy-fifth  part  of  a  single  horse-power,  and  its 
action  thus  represents  the  effect  of  nine  heat-units  per 

*  This  temperature,  as  is  known,  is  about  thirty-seven  degrees 
Centigrade.  Climates  exert  no  influence  in  this  respect;  be- 
tween the  inhabitants  of  the  warmest  countries  and  those  of  the 
coldest  there  is  found  hardly  the  difference  of  a  degree.  The 
kind  of  food  has  itself  no  action  upon  human  temperature.  In 
India  it  is  likewise  thirty-seven  degrees  with  the  native  workmen, 
who  eat  only  rice  and  fish ;  with  the  priests  of  Buddha,  who  live 
on  vegetables,  and  the  soldiers,  fed  chiefly  on  meats.  A  varia- 
tion of  four  or  five  degrees  in  the  average  temperature  of  the 
human  body  constitutes  a  pathological  condition  which  speedily 
terminates  in  death. 


LIVING   BEINGS.  215 

hour.  Many  other  interior  motions  take  place  that 
might  be  estimated  in  the  same  way  with  more  or  less 
exactness  ;  but  the  cycle  of  these  phenomena  being 
accomplished  entirely  within  the  body,  there  is  an 
interior  equivalence  between  the  quantities  of  heat 
and  the  work  they  represent,  and  they  are  not  taken 
into  account  in  the  exchange  which  takes  place  be- 
tween man  and  the  surrounding  medium. 

So  much  for  the  state  of  repose.  Let  us  now  con- 
sider the  man  who  executes  movements,  and  who  pro- 
duces an  external  work. 

The  beautiful  researches  of  M.  Hirn  have  shown 
that  in  the  human  body  heat  is  transformed  into  work, 
and  work  into  heat,  according  to  the  numerical  ratio 
which  we  have  already  so  often  introduced  ;  a  unit  of 
heat  is.  converted  into  four  hundred  and  twenty-five 
kilogrammetres,  and  reciprocally. 

M.  Hirn  has  selected  for  the  object  of  his  investiga- 
tions the  work  which  a  man  produces  in  raising  his 
own  body.  ,  When  we  ascend  a  slope,  or  when  we  de- 
scend it,  our  muscular  force  and  gravity  are  put  in  an- 
tagonism. Practically  this  antagonism  is  complicated 
with  the  horizontal  reactions  due  to  the  friction  neces- 
sary for  walking.  M.  Hirn,  by  an  ingenious  contriv- 
ance, has  succeeded  in  eliminating  this  source  of  com- 
plication, leaving  only  the  vertical  forces  to  be  taken 


2l6        UNITY  OF  NATURAL  PHENOMENA. 

into  account.  Imagine  a  man  moving  along  the  steps 
of  a  movable  wheel ;  if  the  wheel  be  suitably  turned,  the 
man,  without  really  having  to  change  his  place,  will  real- 
ize the  artificial  conditions  of  ascending,  descending,  and 
level  walking,  in  which  vertical  actions  alone  are  put 
into  operation.  The  subject  of  his  experiment  would 
produce  an  external  work  when  displacing  the  centre 
of  gravity  of  his  body  in  order  to  reach  a  higher  step ; 
if  he  descended,  on  the  contrary,  his  weight  would 
operate  as  if  he  had  received  external  work,  and  his 
body  would  profit,  in  some  sort,  by  a  certain  amount 
of  motor  force  ;  if  he  walked  without  ascending  or 
descending,  his  centre  of  gravity  would  be  alternately 
raised  and  lowered  in  equal  degrees  ;  there  would  be 
an  equivalent  production  and  consumption  of  external 
work. 

The  theory  clearly  indicated  the  calorific  effects  that 
should  be  exhibited  under  these  different  circum- 
stances, and  they  were  produced  in  such  a  way  as  to 
fully  justify  the  inductions  of  the  experifhenter.  M. 
Hirn  had  first  established,  by  direct  measurements, 
that  in  a  state  of  repose  every  gramme  of  oxygen  ab- 
sorbed invariably  disengaged  five  heat-units  ;  next,  ob- 
serving the  state  of  motion,  he  saw  that  this  propor- 
tion varied.  If  a  man,  weighing  seventy-five  kilo- 
grammes, raised  his  weight  four  hundred  and  twenty- 


LIVING   BEINGS. 

five  metres,  each  gramme  of  oxygen  disengaged  less 
heat,  and  seventy-five  heat-units,  the  exact  representa- 
tion of  the  work  produced,  disappeared.  If  the  same 
man  descended  four  hundred  and  twenty-five  metres, 
each  gramme  of  oxygen  disengaged  more  than  five 
heat-units,  and  the  descent  thus  left  in  the  organism 
seventy-five  units,  which,  could  not  be  attributed  to 
respiratory  action.  Moreo.ver,  respiration  continued 
to  yield  five  heat-units  per  gramme  of  oxygen  in  the 
case  of  level  walking. 

These  striking  results  have  been  confirmed  by  a 
series  of  repeated  experiments.* 

At  first  thought,  one  may  be  astonished  that  walk- 
ing on  a  level,  as  regards  work,  leads  to  no  expendi- 
ture, and  that  descent  constitutes,  in  this  respect,  a 
sort  of  gain,  seeing  that  both  of  them  —  even  under 
the  conditions  employed  by  M.  Him  —  demand  cer- 
tain efforts,  and  result  in  a  certain  amount  of  fatigue. 
More  than  this,  the  case  of  ascent  may  even  give  rise 
to  an  apparent  objection.  .  How  does  it  happen,  it  may 

*  It  has  been  estimated  that  a  man  of  average  weight  pro- 
duces, in  the  climate  of  France,  three  thousand  J:wo  hundred  and 
fifty  heat-units  per  day,  or  a  sufficient  amount  of  heat  to  raise 
seven  gallons  of  water  to  the  boiling  point.  (See  an  article  from 
the  French  of  Fernand  Papiflon,  in  No.  10  of  the  Popular  Science 
Monthly,  for  interesting  facts  in  regard  to  animal  heat.)  — 
Translator. 


2l8       UNITY  OF  NATURAL  PHENOMENA. 

be  said,  that  the  act  of  ascending  "consumes  heat  when 
the  body  is  manifestly  warmed  in  producing  this  work  ? 
It  is  important  to  do  away  with  these  apparent  contra- 
dictions, which  would  be  of  a  character  to  leave  in  the 
mind  a  vague  distrust  of  the  theory  just  unfolded. 

Yes  ;  the  work  corresponding  to  the  act  of  ascend- 
ing consumes  heat,  but  at  the  same  time  it  accelerates 
the  respiratory  action  and  circulation  ;  the  volume  of 
inspired  air  increases,  and  the  absorbing  power  of  the 
lungs  is  raised  in  a  proportion  often  considerable. 
The  quantity  of  oxygen  absorbed,  consequently  the 
heat  produced,  increases  even  to  five  fold.  M.  Hirn 
has  established  these  facts  by  putting  himself  into  the 
apparatus  which  he  employed  for  his  experiments. 

For  an  ascent  of  four  hundred  and  fifty  metres  per 
hour,  the  number  of  pulsations  of  the  heart  was  raised 
from  eighty  to  one  hundred  and  forty  ;  the  number  of 
respirations  a  minute  went  from  eighteen  to  thirty  ; 
the  body  of  respired  air  in  an  hour  was  augmented 
from  seven  hundred  litres  to  twenty-ldiree  hundred. 
As  a  result  of  this  increasing  activity  in  the  respira- 
tion and  circulation,  the  experimenter  consumed  no 
longer  thirty  grammes,  as  in  a  state  of  rest,  but  even 
one  hundred  and  thirty-two  ^grammes  of  oxygen  per 
hour.  Thus,  in  spite  of  the  consumption  produced  by 


LIVING  BEINGS.  2IQ 

the  work,  an  excess  of  heat  is  developed  within  the 
body,  and  the  individual  becomes  warm. 

Considerations  of  a  like  character  would  do  away 
with  the  difficulty  which  we  pointed  out  with  regard  to 
level  walking  and  descending.  To  speak  only  of  the 
first  case,  every  step  is  divided  into  two  periods  ;  in 
the  one,  the  weight  of  the  body  is  raised,  in  the  other 
it  is  lowered.  The  first  period  consumes  heat ;  the 

second  restores  an  equal  quantity.     Regarded  in  this 

• 
light,  the  calorific  equilibrium  is  not  disturbed  ;  but 

the  organism,  responding  to  the  call  of  the  muscles, 
alternately  contracting  and  elongating,  develops  an 
excess  of  heat.  This  excess  may  be  sufficient  for  an 
interior  work  of  the  muscles  from  which  fatigue  may 
arise,  but  which,  according  to  an  example  already 
given  above,  is  not  at  all  to  be  considered  in  the 
exchange  effected  between  man  and  the  surrounding 
medium. 

The  mechanical  theory,  of  heat  is  then  confirmed 
and  illustrated  in  the  human  motor,  as  in  all  others. 
The  man  who,  in  M.  Hirn's  experiments,  gave  the  best 
dynamic  results  restored  in  work  in  the  ratio  of 
twelve  to  one  hundred  of  the  heat  produced  ;  this  is 
nearly  the  amount  yielded  by  our  most  perfect 
engines. 

If  we  follow  up  this  paralellism  between  the  weight 


22O       UNITY  OF  NATURAL  PHENOMENA. 

of  the  motor  and  the  power  it  develops,  we  still  find  a 
sort  of  equality  between  man  and  our  engines  ;  but 
animated  nature  presents  us,  in  this  respect,  a  class  of 
beings  especially  favored.  These  are  the  birds. 

These  wonderful  motors  evolve  a  force  of  one  horse 
(steam),  while  possessing  a  weight  of  only  five  or  six 
kilogrammes.  Their  physiological  structure,  together 
with  their  relative  lightness,  gives  them  the  means  of 
enduring  the  enormous  work  they  are  obliged  to  pro- 
duce in  order  to  sustain  themselves  in  the  atmosphere. 
The  bird  is  a  centre  of  combustion  of  exceeding  activ- 
ity ;  his  whole  body  is,  so  to  speak,  but  a  lung  ;  the 
air,  powerfully  solicited  through  the  very  play  of  the 
wings,  enters  abundantly  to  vivify  the  blood,  which  the 
heart  impels  with  prodigious  power  through  the  ves- 
sels. The  torrent  of  the  circulation  thus  furnishes  the 
muscles  with  enormous  stores  of  heat,  which  they  are 
able  to  convert  into  work.  Thus,  while  the  tempera- 
ture of  man  remains  fixed  at  about  ninety-eight  de- 
grees Fahrenheit,  that  of  the  bird  reaches  one  hundred 
and  nine  to  one  hundred  and  eleven  degrees.  It  ex- 
ceeds, consequently,  the  limits  beyond  which  our 
organs  become  unfitted  for  life.  It  has  been  proved 
that  the  bird  consumes,  in  a  state  of  repose,  a  great 
quantity  of  oxygen  ;  one  would  undoubtedly  be  aston- 
ished if  it  were  possible  to  ascertain  how  much  it  ab- 


LIVING   BEINGS.  221 

sorbs  in  rapid  flight.  Let  us  add  that,  in  order  to 
endure  this  active  combustion,  the  bird  must  be  able 
to  repair  promptly  the  losses  it  suffers.  Its  organs  of 
nutrition  respond  to  this  necessity.  Its  gizzard,  hard 
as  horn,  grinds  without  difficulty  the  most  resisting 
articles  of  food  ;  a  liver  of  great  size  pours  forrents  of 
bile  over  the  material  which  comes  from  the  gizzard, 
and  digestion  is  effected  with  surprising  rapidity.  So 
the  bird  cannot  go  hungry.  It  is  sometimes  remarked 
of  a  person  who  takes  but  little  nourishment  that  he 
eats  like  a  bird.  Jlris  is  a  phrase  to  be  taken  with 
reservation,  and  one  that  should  undoubtedly  be  re- 
moved from  our  vocabulary.  The  species  which  feed 
on  living  prey  make  a  very  great  slaughter  ;  those 
which  live  on  fruits  and  grains  eat  a  little  at  a  time 
perhaps,  but  it  is  on  the  condition  of  finding  the  table 
always  spread. 


222       UNITY  OF  NATURAL  PHENOMENA. 

III. 

Muscular  Contraction  and  Innervation. 

WE  have  just  established  in  the  case  of  man,  and 
incidentally  in  the  case  of  birds,  the  conversion  of  heat 
into  work.  We  must  again  examine,  a  little  more 
closely,  the  circumstances  which  accompany  this  phe- 
nomenon. 

The  muscles  swell  up,  and  become  shortened,  to 
effect  the  motions  of  the  bones  Jo  which  they  are 
attached. 

When,  in  physiological  experiments,  a  muscle  is 
made  to  contract  by  an  artificial  irritation,  pinching  it, 
for  example,  or  communicating  to  it  an  electric  shock, 
there  result  jerks  and  violent  contractions,  which  do 
not  resemble  the  regular  motions  which  the  will  calls 
into  action ;  but  if  a  continued  series  of  irritations  be 
kept  up,  the  muscle  *  is  observed  to  contract  in  a 

*  Muscles  are  composed  of  fibres,  which  are  contractile  in  a 
a  high  degree,  and  which  occur  under  two  principal  forms  :  the 
smooth  fibre  belongs  to  the  muscles  which  serve  the  purposes 
of  organic  life,  to  that  silent,  and  as  it  were,  unconscious  life, 
which  animates  the  various  parts  of  the  body;  the  striped  fibre 
belongs  to  the  muscles  of  the  life  of  relation,  those  which  produce 
the  voluntary  motions.  Certain  muscles,  the  heart,  for  example, 
present  a  mixed  composition.  There  would  appear  to  be  a  dif- 


LIVING  BEINGS.  223 

permanent  manner.  Helmholtz,  employing  the  inter- 
rupted current  of  an  induction  coil,  has  shown  that  at 
least  twenty-two  excitations  per  second  are  needed  to 
secure  continued  contraction. 

The  muscle  thus  contracted  gives  out  a  percepti- 
ble, though  very  deep  sound.  Helmholtz  was  able-  to 
prove  that  the  pitch  of  this  sound  corresponded  to 
the  number  of  interruptions  produced  in  the  induction 
coil. 

There  is,  besides,  a  characteristic  fact  that  accom- 
panies muscular  contraction,  one  that  may  be  regarded 
as  its  direct  cause ;  it  is  a  powerful  absorption  of  oxy- 
gen. M.  Matteucci  proved  this  by  comparing,  in  a 
lime-water  bath,  the  amount  of  carbonic  acid  given 
out  by  muscles,  when  contracted,  and  when  in  a  state 
of  rest.  The  oxidation  of  muscles  is  likewise  directly 
observed  in  the  animal  economy;  it  is  known  that 
the  venous  blood,  when  it  comes  from  muscles  a  long 
time  contracted,  is  completely  deprived  of  oxygen,  and 
contains  a  large  excess  of  carbonic  acid. 

Thus  there  is  no  doubt  in  regard  to  this.     What 

ference  in  the  mobility  of  these  two  kinds  of  fibres.  The  striated 
muscle,  when  irritated,  contracts  abruptly,  and  relaxes  imme- 
diately; the  smooth  fibre  acts  more  slowly,  and  in  a  more  pro- 
longed manner.  Physiology  has  chiefly  studied  the  striped  mus- 
cles; it  is  these  which  possess  the  highest  importance  for  us  at 
this  time,  since  they  are  the  instruments  of  voluntary  motion. 


224       UNITY  OF  NATURAL  PHENOMENA. 

designates  Contraction  is  an  increase  of  energy  in  the 
oxidation  of  the  muscular  tissues,  a  more  active  de- 
composition of  the  hydrocarbonated  materials  by  the 
elements  of  the  arterial  blood.  That  chemical  action 

thus   set   up   throughout   the   extent   of  the    muscle 

• 
changes  its  form,  that  it  shortens  the  muscle  while 

increasing  it  in  size,  is  not  a  matter  of  astonishment 
to  us  ;  we  often  see  a  rope  swell  up  and  become  tight 
when  it  is  wet,  and  produce  in  this  way  a  considerable 
traction.  That  the  heat  developed  in  muscular  tissue 
should  be  partially  converted  into  work,  is  what  we 
also  regard  as  an  ordinary  and  common  phenomenon. 
M.  Beclard  has,  moreover,  made  a  series  of  ingenious 
experiments  upon  this  matter.  He  has  studied,  in  its 
calorific  bearing,  the  same  muscular  contraction  in  the 
case  where  it  produces  no  external  work,  and  in  the 
case  where  it  does  ;  he  thus  observed,  during  a  long 
series  of  experiments,  that  the  heat  due  to  chemical 
action  was  diminished  by  just  that  amount  which  was 
transformed  into  work. 

But  let  us  not  stop  here  ;  let  us  endeavor  to  go  back 
to  the  origin  of  muscular  action. 

The  nerves  interpose  to  excite  the  .action  of  the 
muscles. 

The  nervous  system,  if  we  regard  it  in  its  relations 
to  motion,  may  be  represented  in  the  following  man- 


LIVING   BEINGS.  22$ 

ner.  An  external  organ  receives  the  sensations ;  a 
very  slender  tubular  filament  carries  them  to  a  nerve 
cell  which  perceives  them  ;  another  cell,  suited  to 
direct  movements,  communicates  by  means  of  a  new 
filament  with  the  contractile  apparatus  that  is  to  exe- 
cute them  ;  finally,  a  nerve  tube  acts  as  a  bond  of 
union  between  the  cell  which  receives  the  impressions 
and  the  motor  cell.  Such,  reduced  to  its  simplest 
expression,  is  the  general  idea  of  nervous  communi.ca- 
tion.  The  act  which  is  propagated  from  one  extremi- 
ty to  the  other  of  the  system  is  termed  a  reflex  act. 
The  elementary  filaments,  very  thin  and  delicate, 
since  a  great  number  of  them  possess  a  thickness  of 
scarcely  a  hundredth  part  of  a  millimeter,  are  bound 
together  and  intertwined  in  such  a  way  as  to  form 
little  cords ;  the  cells  are  also  grouped  together  at 
certain  points,  which  bear  the  name  of  nervous  cen- 
tres. With  vertebrates,  with  man,  whom  we  have 
especially  in  view,  the  greater  number  of  these  ner- 
vous centres  are  united  together  in  that  long  stem, 
which  constitutes  the  spinal  marrow.  Nevertheless 
a  certain  number  remain,  which  are  scattered  through- 
out the  body  ;  these  are  called  nervous  ganglions,  and 
taken  together  they  are  known  under  the  name  of  the 
great  sympathetic  system.  A  sort  of  hierarchy  is  thus 
established  in  the  reflex  actions  ;  some  concern  the 


226       UNITY  OF  NATURAL  PHENOMENA. 

ganglions  only,  while  others  reach  as  far  as  the  -spinal 
marrow.  Above  this  rises  a  still  higher  system.  At 
the  origin  of  the  encephalon  are  found  the  oval  masses, 
which  preside  over  the  respiratory  movements  and 
the  .contractions  of  the  heart ;  next  comes  the  cere- 
bellum, which  co-ordinates  the  voluntary  motions,  then 
the  lobes  of  the  brain,  where  the  will  and  the  intellect 
reside.  First  the  ganglions,  afterwards  the  spinal  mar- 
row, make  successively  a  sort  of  selection  from  among 
the  reflex  acts,  permitting  only  a  certain  number  of 
them  to  reach  the  higher  regions  of  the  system  where 
would  seem  to  be  concentrated  the  conscious  govern- 
ing power  of  the  being.  Thus  may  be  reduced  to  a 
few  general  outlines  the  infinite  complication  of  this  so 
delicate  network  which  ramifies  throughout  the  whole 
extent  of  the  body. 

How  is  nervous  action  propagated  ? 

Several  years  ago  the  works  published  by  M.  Du 
Bois  Reymond,  and  several  German  physiologists) 
seemed  to  have  solved  this  problem.  A  solution 
which  offered  itself,  under  such  an  attractive  exterior, 
was  accepted  with  eagerness.  Innervation  was  an 
electric  current.  A  current  was  transmitted  along  the 
sensitive  nerve  to  end  in  the  cell  of  sensation ;  a 
current  quitted  the  motor  cell  in  order  to  end  in  the 
organ  of  motion ;  whatever  might  have  been  the  re- 


LIVING  BEINGS.  22/ 

actions  effected  within  the  cells,  they  assumed,  hence- 
forth, a  manifest  analogy  with  that  which  takes  place 
in  a  battery,  or  other  electro-motor  machine. 

The  excitement  over  this  explanation  cooled  off. 
Admitted  at  the  outset,  with  insufficient  proof,  it  was 
finally  rejected  by  many  physiologists  without  suffi- 
ciently good  reasons.  We  do  not  find  in  the  human 
body  the  simple  conditions  presented  by  our  electrical 
apparatus.  It  is  clear  that  a  nerve  cannot  be  entirely 
analogous  to  an  insulated  conducting  arc,  since  it  is 
itself,  like  everything  around  it,  the  seat  of  incessant 
reactions.  One  was  too  readily  discouraged  by  reason 
of  the  confusion  in  the  results  yielded  by  experiments. 
To  invalidate  the  existence  of  nervous  currents,  reasons 
are  brought  forward  which  do  not  appear  to  have  great 
weight.  Electric  currents,  it  is  said,  are  transmitted 
slowly  in  the  nerves,  having  only  a  velocity  of  twenty- 
four,  or  eve*  of  eighteen  metres  in  a  second  ;  they  go 
less  rapidly  in  the  nerves  than  in  the  muscles.  It  is 
argued  again  that  a  nerve,  when  cut,  however  closely 
the  ends  may  be  applied  to  each  other,  becomes  unfit 
for  communication.  These  are  matters  which  have 
nothing  of  a  decisive  character.  Whatever  may  be 
said,  we  find  ourselves  still  confronted  with  important 
and  highly  significant  facts.  By  causing  electric  cur- 
rents to  act  upon  a  nerve,  —  veritable  currents  produced 


228       UNITY  OF  NATURAL  PHENOMENA. 

by  our  machines,  -*-  we  obtain  the  contraction  of  mus- 
cles ;  not  an  instantaneous  contraction  alone,  but  a 
continued  one.  Let  one  take  the  hinder  parts  of  a 
frog,  the  two  thighs  attached  to  the  lumbar  nerves, 
and  these  latter  to  a  fragment  of  the  spinal  marrow, 
and  let  a  current  be  passed  along  one  of  the  nerves, 
and  there  will  follow  not  only  a  direct  excitation  of 
the  corresponding  limb,  but  also  the  reflex  motion  of 
the  other  thigh. 

It  seems  to  us  that  these  results,  well  known  and 
within  the  reach  of  common  experience,  furnish  seriT 
ous  grounds  for  conviction.  Now,  if  it  be  proved  that 
the  stream  which  reaches  the  muscles  is  not  to  be 
confounded  with  the  electric  current,  that  it  is  to  be 
regarded  as  possessing  a  special  character,  and  to  be 
studied  under  a  distinct  name,  there  will  yet  be  noth- 
ing in  this  circumstance  that  can  weaken  the  results 
we  present.  Under  cover  of  this  declaration,  we  con- 
tinue to  speak  of  nervous  action  as  of  an  electric  cur- 
rent. It  will  be  possible,  if  so  desired,  to  see  in  this 
language  merely  a  figurative  representation  of  the  phe- 
nomena ;  it  will  be  sufficiently  exact  to  justify  the 
results  we  wish  to  illustrate. 

Thus  the  nerve  excites  the  muscle.  Does  this  mean 
that  the  nerve  possesses  in  itself  all  the  energy  which 
is  developed  in  the  muscle  ?  No ;  since  the  muscle 


LIVING   BEINGS.  22Q 

gets  this  fouce  directly  by  its  own  oxidation.  The 
nerve  merely  excites  chemical  action  ;  it  only  sets  go- 
ing a  piece  of  machinery.  It  is  thus  that  a  spark  pro- 
duces the  explosion  of  a  gaseous  mixture ;  it  is  thus 
that  a  match  effects  the  lighting  of  a  fire  ;  it  is  thus, 
by  turning  a  stop-cock,  that  we  let  flow  away  all  the 
water  accumulated  in  a  reservoir. 

One  is  naturally  led  to  think  that  the  work  of  the 
nerve  is  exceedingly  small  compared  to  that  of  the 
muscle.  M.  Matteucci  has  proved  this  a  fact  by  direct 
experiment.  He  hung  a  weight  to  the  principal  mus- 
cle of  the  leg  of  a  frog,  and  sent  an  electric  current 
through  the  nerve  attached  to  this  muscle.  The  con- 
traction of  the  muscle  raised  the  weight,  and  it  was 
easy  to  estimate  the  effort  in  foot-pounds.  Likewise, 
by  a  simple  calculation,  might  be  estimated  the  com- 
bustion of  the  zinc  produced  in  the  battery  during 
the  very  brief  period  of  excitation.  M.  Matteucci 
thus  found  the  work  done  by  the  muscle  to  be  at  least 
twenty-seven  thousand  times  greater  than  the  chemi- 
cal or  calorific  effect  of  the  nervous  excitation. 

Let  us  go  back  yet  farther,  and  approach  the  origin 
of  the  motion.  Small  as  the  work  of  the  nerve  may 
be,  how  is  it  accomplished  ?  To  give  rise  to  a  cur- 
rent in  a  nerve,  it  is  enough  that  a  circuit  be  formed 
somewhere,  either  within  or  on  the  outside  of  the 


23O       UNITY  OF  NATURAL  PHENOMENA. 

nerve  cell,  and  this  action  itself  is  only,  a  very  slight 
portion  of  the  action  which  the  current  can  produce. 
As  to  the  mode  in  which  such  a  circuit  is  formed, 
nothing  definite  can  be  known.  If  it  be  a  question  of 
voluntary  motion,  we  say  that  the  will  intervenes. 

But  two  things  are  to  be  noted. 

First,  the  mechanical  action  attributed  to  the.  will 
becomes,  from  the  preceding  considerations,  gradually 
reduced  to  one  so  extremely  minute  that  it  seems  to 
disappear  altogether. 

Let  us  add,  in  the  second  place,  that  the  will  does 
not  create  this  work,  however  imperceptible  it  may  be. 
It  can  only  be  conceived  of  as  a  special  agent  of 
transformation  in  motions  infinitely  small.  The  vol- 
untary act,  —  and  for  a  still  stronger  reason  the  purely 
reflex  act,  —  to  whatever  degree  of  tenuity  it  be  re- 
duced, does  not  proceed  without  a  subtle  modification 
of  the  tissues  in  which  it  is  effected,  without  I  know 
not  what  sort  of  delicate  transformation  of  molecular 
motions. 

In  ascending  from  muscular  action  to  nervous  ac- 
tion, properly  so  called,  and  to  the  play  of  the  will,  we 
have  reached  the  limit  where  physical  phenomena 
give  place  to  moral,  and  beyond  this  we  have  not  to 
pass. 

Within  the  limits  we  have  now  reached  we  have 


LIVING  BEINGS.  23! 

been  able  to  show  how  the  principles  to  which  we 
have  been  led  by  the  study  of  the  inorganic  ;world  are 
verified  in  the  case  of  living  beings.  Our  conception 
of  the  physical  universe  would  have  been  too  incom- 
plete had  we  been  obliged  to  curtail  from  it  all  that 
pertains  to  life. 

We  may  now,  without  leaving  behind  us  so  formida- 
ble a  gap,  resume  the  synthesis  we  have  undertaken, 
and  endeavor  to  give  it  its  final  shape. 


232  UNITY  OF   NATURAL   PHENOMENA. 


CHAPTER  VII.. 
CONCLUSION. 

CUVIER  said,  in  his  History  of  the  Progress  of  the 
Natural  Sciences,  "  Once  having  quit  the  phenomena 
of  shock,  we  no  longer  possess  any  clear  idea  of  the  re- 
lations of  cause  and  effect.  Everything  is  reduced  to 
the  collecting  of  particular  facts,  and  the  searching  out 
of  the  general  propositions  which  embrace  the  greatest 
number  of  them.  It  is  in  this  that  all  physical  theo- 
ries consist,  and,  to  whatever  degree  of  generality 
each  of  them  may  have  been  reduced,  they  will  still  be 
far  from  a  conformity  with  the  laws  of  shock,  which 
alone  could  change  them  into  real  explanations." 

It  cannot  be  said  that  physicists  have  already  ful- 
filled the  programme  marked  out  by  these  words. 
And  yet,  if  we  cast  a  look  behind  over  the  road  we 
have  traversed,  and  include  in  a  general  view  all  the 
facts  we  have  mentioned,  we  shall  feel  more  and 
more  established  in  this  idea,  that  all  physical  phe- 
nomena consist  in  the  exchange  and  transformation  of 
material  motions. 


CONCLUSION.  233 

Will  it  be  said  that  our  examination  has  not  always 
been  rigid  enough  ?  that  we  have  sometimes  asserted, 
when  we  ought  to  have  expressed  a  doubt  ?  that  we 
have  not  always  laid  sufficient  stress  upon  the  reserva- 
tions we  were  led  to  make?-  We  shall  not  try  to 
shield  ourselves  from  this  censure,  feeling  too  well 
that  we  have  deserved  it.  It  would  have  been  better, 
perhaps,  to  have  left  more  points  in  obscurity,  and  to 
have  limited  ourselves  to  certain  facts.  May  we  be 
pardoned  for  some  suggestions  too  conjectural  ?  The 
results  acquired  are  considerable,  and  a  few  rash  sup- 
positions cannot  compromise  them. 

These  acquired  results  we  could  at  need  clothe  with 
the  authority  of  an  eminent  man  of  science.-  M.  De 
Senarmont,  during  the  last  year  of  the  lectures  which 
he  delivered  with  so  much  brilliancy  at  the  Ecole  Poly- 
tecJinique,  and  which  death  came  so  early  to  interrupt, 
thus  summed  up  his  views  upon  the  progress  of  the 
physical  sciences  :  "  Even  lately  each  group  of  facts 
acknowledged  a  special  principle.  Motion  and  rest 
resulted  from  forces,  ill-defined  enough  specifically, 
but  which  it  was  agreed  to  term  mechanical ;  the  phe- 
nomena of  heat,  light,  electricity,  badly  enough  defined 
themselves,  were  produced  by  so  many  particular 
agents,  fluids  endowed  with  special  activities.  A 
more  searching  examination  has  enabled  us  to  dis- 


234       UNITY  OF  NATURAL  PHENOMENA. 

cover  that  this  noticfn  of  a  variety  of  specific  and 
heterogeneous  agents  has  at  bottom  -only  a  solitary 
and  unique  basis  ;  this  is,  that  the  perception  of  these 
various  kinds  of  phenomena  is  in  general  effected 
through  the  different  organs,  and  that  in  addressing 
themselves  more  particularly  tc  each  of  our  senses, 
they  necessarily  excite  particular  sensations.  The  ap- 
parent heterogeneity  would  then  be  less  in  the  nature 
itself  of  the  physical  agent  than  in  the  functions  of 
the  physiological  instrument  which  shapes  the  sensa- 
tions ;  so  that  in  falsely  attributing  the  dissimilarities 
in  the  effect  to  the  cause,  we  should  have  in  reality 
classified  the  intermediate  phenomena  through  which 
we  have  a  knowledge  of  the  modifications  of  matter, 
rather  than  the  essence  itself  of  these  modifications. 
.  .  .  All  physical  phenomena,  whatever  their  nature, 
appear  at  bottom  to  be  only  manifestations  of  one  and 
the  same  primordial  agent.  .  .  .  This  general  result 
of  all  modern  discoveries  can  no  longer  be  ignored, 
however  impossible  it  may  still  be  to  put  into  definite 
shape  their  laws  and  their  conditional  details." 

Such  was  the  language  of  M.  De  Senarmont  in  a 
course  of  academical  instruction,  in  which  no  room 
was  allowed  for  any  unsafe  doctrine. 

We  are  not  bound  to  a  like  reserve.  So  we  have 
more  explicitly  stated  the  system  which  seems  to  sum 


CONCLUSION.  235 

up  the  labors,  and  to  express  the  general  sentiment  of 
contemporary  physical  science.  Ether  in  a  state  of 
motion  fills  all  space.  The  ethereal  atoms,  by  their 
aggregation,  form  molecules  ;  these  last,  bodies.  Be- 
tween these  atoms,  these  molecules,  these  bodies,  inter- 
changes of  motion  take  place,  constituting  what  we 
term  heat,  light,  electricity,  gravity,  chemical  affinity. 
These  interchanges  depend  upon  the  masses  and  ve- 
locities which  are  concerned.  The  conception  of  the 
physical  universe  is  contained  entirely  in  these  prin- 
ciples. Hitherto  we  have  been  able  to  get  but  a  very 
small  number  of  the  facts  which  this  statement  of 
principles  embraces,  because  we  are  unacquainted, 
nearly  always,  both  with  the  absolute  and  the  relative 
values  of  the  masses  and  velocities  which  govern  the 
communication  of  motions.  Practically  we  are  satis- 
fied with  saying  that  heat,  light,  electricity,  gravity, 
affinity,  are  transformed  into  each  other  according  to 
the  fixed  relations  of  equivalence,  and  we  assign  them 
a  common  measure,  that  of  mechanical  work. 

Left  thus  on  the  outside  of  phenomena,  we  have  but 
a  vague. notion  of  the  circumstances  that  accompany 
and  determine  transformations.  There  are,  doubtless, 
motions  to  which  we  are  unable  to  give  a  name,  and 
which  we  are  not  qualified  to  perceive,  although  they 
play  their  part  in  nature. 


236       UNITY  OF  NATURAL  PHENOMENA. 

Amid  the  variety  and  number  of  motions  that  would 
seem  possible,  why  are  some  produced  and  not 
others  ? 

Is  there  among  motions  a  sort  of  natural  selection  ? 

We  should  possess  the  key  of  the  transformations 
taking  place  under  our  eyes  if  we  could  attain  to  that 
measurement  of  the  masses  and  velocities  which,  until 
now,  eludes  us.  In  a  steam  .engine,  for  example,  the 
agitation  which  reigns  in  the  heat  of  the  furnace  is 
communicated  to  the  tubes  of  the  boiler,  and  from 
these  to  the  water  itself ;  the  molecules  of  vaporized 
water  each  expend  a  little  of  their  living  force  upon 
the  piston,  which  moves  under  these  accumulated 
efforts,  and  sets  in  motion  the  shaft  of  the  engine  ; 
but  we  perceive  this  series  of  changes  only  through  a 
veil.  When  a  motion  of  a  certain  kind  is  replaced  by 
another  of  a  different  kind,  the  reason  for  this  ex- 
change usually  escapes  us  ;  and  it  is  because  of  this 
ignorance  that  we  have  recourse  to  the  idea  of  force  ; 
we  say  that  a  force  is  exhibited,  and  produces  such  an 
effect,  because  we  are  unable  to  grasp  the  anterior 
motions  from  which  this  effect  results. 

The  notion  of  physical  force  ought  then  to  disap- 
pear if  the  elements  of  molecular  mechanics  were 
known.  In  the  present  state  of  our  knowledge  we 
must,  indeed,  preserve  it ;  but  we  must  also  be  on  our 


CONCLUSION.  237 

•  ,t  » 

guard  against  the  errors  it  may  entail.  Let  us'  call 
force  every  cause  of  motion,  if  it  be  desired  ;  but  let 
us  not  forget  that  this  word  most  generally  represents 
only  a  provisional  and  conditional  cause.  The  dread 
of  a  vacuum  has  been  a  force  in  its  time,  that  is,  of  a 
vacuum  to  the  extent  of  thirty-two  feet. 

If  we  recur  with  persistence  to  this  consideration, 
it  is  because  it  seems  to  us  to  be  of  capital  impor- 
tance, and  we  could  not  devote  too  great  an  effort  to- 
wards its  illustration.  It  is  the  knotty  point  in  the 
system  we  have  unfolded.  And  yet,  among  the  phys- 
icists even  who  have  entered  into  the  current  of  new 
ideas,  there  is  a  school  which  persists  in  giving  to 
the  physical  forces  an  unaccountable  individual  ex- 
istence. 

M.  Hirn,  whose  name  in  France  is  connected  with 
the  determination  of  the  mechanical  equivalent  .of 
heat ;  M.  Hirn,  whom  we  mention  when  we  wish  to 
place  a  French  name  by  the  side  of  those  of  MM. 
Joule  and  Mayer^;  M.  Hirn  does  not  hesitate  to  re- 
gard the  physical  forces  as  the  constituent  elements 
of  the  universe.  Under  the  title  of  intermediate  prin- 
ciples, he  makes  of  them  half  transcendental  essences, 
which  fill  all  space,  and  which  have  the  property  of 
conferring  motion  jipon  matter.  He  even  makes  an 
enumeration  of  these  principles,  and  finds  four  of 


238       UNITY  OF  NATURAL  PHENOMENA. 

» 

them  gravity-force,  light-force,  heat-force,  and  electric- 
force. 

What !  does  matter  here  and  there  quit  its  state 
of  rest,  and  do  new  motions  spring  up  at  the  will  of 
these  forces  ?  This  is  not  precisely  what  M.  Hirn 
means ;  he  knows  too  well  it  would  be  in  contradiction 
with  the  facts.  Here  is  the  theory  he  conceives.  For 
him  each  force  is  everywhere  diffused.  At  the  instant 
the  intensity  of  one  increases  in  such  a  way  as  to  pro- 
duce a  motion,  the  intensity  of  another  force  dimin- 
ishes in  a  corresponding  ratio.  Now  this  diminution 
of  intensity  in  the  second  force  itself  corresponds  to  a 
diminution  of  motion  in  matter.  It  is,  evidently,  a 
sort  of  pre-established  harmony.  Doubtless  we  have 
but  to  suppress  these  artificial  intermediate  agents,  to 
find  ourselves  face  to  face  with  motions  themselves, 
and  the  return  is  thus  easy,  when  it  is  desired,  from 
M.  Hirn's  stand-point  to  that  we  just  now  occupied. 
Why  introduce,  hereafter,  between  two  motions  which 
beget  each  other,  two  semi-transcendental  essences  ? 
Why  have  recourse  to  these  intermediate  principles  ? 
Why  this  mythology,  this  Olympus  of  forces  ? 

Why  ?  It  is  not  very  hard  to  give  the  reason,  nor 
will  it  be  useless  to  do  so. 

These  arbitrary  conceptions  are  inspired  in  M.  Hirn 
by  the  disturbing  influence  of  an  easily  alarmed  spirit- 


CONCLUSION.  239 

ualism.  M.  Hirn  becomes  distrustful  when  he  sees  a 
doctrine  which  every  day  explains  by  the  motions  of 
matter  an  ever-increasing  number  of  facts.  He  dreads 
the  encro'achment  He  fears  lest  it  may  come  to 
reach  the  human  soul ;  lest  it  reduce  to  pure  motions 
the  phenomena  of  will  and  of  thought.  It  is  for  the 
purpose  of  arresting  it  in  its  progress  that  he  has  re-' 
course  to  gravity,  heat,  light,  and  electric  forces. 
These  intermediate  principles  are  the  bulwarks  he 
raises  to  defend  the  soul-principle.  Strange  bulwarks 
in  tputh,  and  far  from  capable  of  such  a  defence ! 
Must  it  be  repeated,  moreover,  that  the  problems  of 
the  soul  are  in  no  way  concerned  in  the  theories 
against  which  M.  Hirn  endeavors  to  fortify  himself? 
In  the  midst  of  material  transformations,  causes  active 
in  themselves  may  interfere,  and  we  have  pointed  out 
examples  of  them  in  indicating  the  nature  and  limits 
of  this  interference.  This  is  sufficient  to  leave  the 

• 

field  free  for  all  the  solutions  of  metaphysics. 

Having  shown  how  our  hypothesis  banishes  the  fal- 
lacious entities  with  which  physical  science  may  be 
encumbered,  is  there  need  of  defending  the  theory 
itself  from  the  extravagant  deductions  that  might  be 
drawn  from  it  ?  Is  there  need  of  indicating  the  point 
of  view  from  which  an  entirely  healthy  conception  of 
it  is  to  be  obtained  ? 


24O       UNITY  OF  NATURAL  PHENOMENA. 

Is  admitting  a  scientific  hypothesis  equivalent  to 
believing  one's  self  in  possession  of  the  realities  of 
things  ?  This  would  be,  too  easily  forgetting  so  many 
systems  that  have  buried  each  other  in  their  ruins. 
It  would  be  forgetting  too  easily  that  the  physical 
philosopher,  lost  in  the  infinity  of  time  and  space, 
seizes  only  apparent  relations,  and  does  not  even  ar- 
rive at  a  conception  of  the  absolute  !  What,  then, 
is  it  to  group  together  into  an  hypothesis  all  our  ideas 
concerning  nature?  It  is  to  afford  us  the  means  of 
illustrating  the  things .  we  learn  by  comparing  them 
with  each  other,  of  establishing  fruitful  relationships 
between  facts,  and  so  cause  springs  of  discovery -to 
burst  forth. 

What  is  of  importance,  correctly  speaking,  in  such 
an  hypothesis,  is  not  the  picture  it  gives  of  nature, 
but  the  plan  it  traces  out  for  the  explorer  of  physi- 
cal science. 

In  this  connection,  the  system  we  have  exhibited  is 
admirably  summed  up  in  a  solitary  principle.  It 
evolves  a  luminous  criterion,  whose  efficiency  has  al- 
ready been  revealed  in  scientific  researches. 

This  precious  symbol  has  a  name  in  the  language 
of  mechanics  ;  but  before  pronouncing  it,  let  us  hasten 
to  recall  to  mind  what  we  have  already  said  regarding 
the  difficulty  one  encounters  of  expressing  new  ideas 


CONCLUSION.  241 

with  old  words.  By  a  cruel  irony  of  circumstances^ 
we  are  about  to  fall  in  with  a  word  we  would  like  to 
have  escaped  from  at  this  time  by  reason  of  the  am- 
biguity it  contains.  Never  have  we  more  keenly  felt 
the  need  of  employing  a  new  expression,  and  if  we 
refrain  from  so  doing,  it  is  for  the  reason  that  our 
declaration  in  this  regard  will  doubtless  stand  us  in 
stead  of  a  neologism.  We  conceive  the  presence 
in  the  universe  of  an  unchanging  supply  of  ma- 
terial atoms  endowed  with  rapid  motion,  and  group- 
ing themselves  into  systems  to  form  molecules  and 
bodies.  Each  of  the  atoms  and  systems  possesses,  in 
proportion  to  its  mass  and  velocity,  what  we  have  hith- 
erto termed  a  living  force,  —  what  we  may  now  call, 
if  we  desire  to  avoid  this  ambiguous  term,  an  energy, 
without  gaining  much  by  the  change.  Such  are  the 
expressions  against  which  we  have  desired  to  take  pre- 
cautions by  a  preliminary  statement.  We  do  not  em- 
ploy a  new  word ;  but  we  have  said  enough  to  show 
that  under  these  usual  designations,  we  are  to  see  ab- 
solutely only  masses  in  motion.  To  say  that  energy 
changes  its  locality,  is  merely  to  say  that  masses  act 
upon  each  other  in  mutually  modifying  their  velocity. 

Energy  thus  passes  without  limitation  from  one  sys- 
tem to  another,  thus  giving  origin  to  the  variety  of 
natural  phenomena.     Sometimes  it  shows  itself  in  a 
16 


242       UNITY  OF  NATURAL  PHENOMENA. 

«  series  of  changes,  in  which  its  successive  efforts  may 
be  followed  ;  then  it  is  said  to  preserve  the  active  form> 
Sometimes  it  hides  itself  in  order  to  maintain,  for  a 
longer  or  shorter  period,  an  equilibrium,  whose  rupture 
will  regenerate  it ;  it  is  then  said  to  pass  into  the  po- 
tential  state.  Active  energy  and  potential  energy 
vary  incessan-tly  in  their  relative  proportion,  but  their 
sum  remains  constant. 

Such  is  the  principle  usually  designated  under  the 
name  of  conservation  of  energy. 

Doubtless,  in  order  to  verify  entirely  this  constancy 
of  energy,  it  would  be  necessary  to  include  the  whole 
universe.  Energy  may  increase  at  certain  periods,  in 
certain  regions  of  space,  and  decrease  in  different  re- 
gions, though  the  ether  would  appear  to  be  a  sort  of 
regulator  of  this  universal  activity.  Do  the  changes 
which  unceasingly  take  place  between  our  terrestrial 
globe  and  the  sidereal  medium  become  interpreted  to 
us  by  a  loss,  by  a  gain,  by  a  periodic  oscillation  about 
a  mean  condition  ?  How  does  our  solar  system  com- 
port itself  with  reference  to  other  systems  ?  Such 
are  the  vast  problems  to  which  the  notion  of  universal 
energy  finds  its  application. 

We  do  not  mean  that  the  principle  of  the  coftserva- 
tion  of  energy  cannot  be  verified  in  the  immediate 
connection  of  ordinary  phenomena.  It  establishes  a 


CONCLUSION.  243 

definite  bond  of  union  between  all  the  facts  which 
surround  us.  The  physical  philosopher  knows  that 
motions  can  pass  from  visible  masses  to  invisible  ones, 
without  ceasing  to  obey  a  law  whose  purport  he 
knows.  If  he  is  not-  always  fortunate  enough  to 
gather  the  facts  into  complete  cycles,  where  effects 
and  causes  are  linked  into  a  chain  whose  ends  meet, 
at  least  he  is  no  longer  forced  to  regard  phenomena 
as  isolated  appearances.  In  the  case  of  each  one  he 
is  able  to  ascend  to  its  sources,  or  descend  to  its  con- 
sequences. He  may  fail  in  the  application  of  his 
method,  he  may  represent  to  himself  in  a  false  light, 
this  or  that  family  of  facts,  but  the  principle  itself, 
by  virtue  of  which  he  seeks  a  fundamental  unity  be- 
neath the  infinite  diversity  of  appearances,  is  to  him 
the  most  precious  and  the  best  assured  conquest  of 
contemporary  science. 


INDEX. 


A. 

ABSOLUTE  zero  of  temperature,  120. 

Acoustics,  experiments  in,  71. 

Affinity,  how  explained  by  the  new  theory,  200. 

Agassiz,  Louis,  recognizes  the  divine  providence  in  nature,  20. 

Anaximenes  regards  air -as  the  primitive  element,  47. 

Arago,  his  explanation  of  light  interferences,  68. 

Aristotle  regards  matter  as  identical,  n. 

Astronomy,  history  of,  169,  et  seq. 

Atmospheres,  ethereal,  how  they  envelop  the  atoms,  114. 

Atoms  not  elastic,  77. 

Attraction  and  repulsion  due  to  ethereal  shocks,  157. 

Attractive  forces  not  inherent  in  matter,  155.* 


B. 

Beclard,  his  experiments  upon  muscular  contraction,  224. 

Bernouilles,  his  Hydronamics,  115. 

Billiards,  game  of,  illustrates  the  motions  of  translation  and  ro- 
tation, 78. 

Birds,  amount  of  heat  evolved  in,  220. 

Birds,  temperature  of,  220. 

Birds,  their  rapid  digestion,  221. 

Boucheporn,  M.  de,  his  law  of  three  squares,  84. 

Boucheporn,  M.  de,  his  theory  of  the  cause  of  colors,  82. 

Boucheporn,  M.  de,  his  treatise  upon  a  general  principle  in 
natural  philosophy,  27. 

244 


INDEX.  245 

« 
Boucheporn,  M.  de,  his  views  regarding  the  transversal  motion 

of  the  ether,  Si. 

Boucheporn,  M.  de,  on  the  inter-atomic  spaces,  91.. 
British  Association  and  the  submarine  telegraph,  131. 


c. 

Carbon,  sulphide  of,  how  the  solar  raj  is  affected  by  passing 
through  a  prism  of,  63. 

Carnot,  Sadi,  on  the  motive  power  of  fire,  104. 

Carpenter,  Dr..  refers  the  origin  of  all  power  to  mind,  20. 

Cartesians,  their  dispute  with  the  Newtonians,  183. 

Cassini,  his  curve  of  the  sidereal  motions,  182. 

Cassinoid,  the,  182.  % 

Cauchj,  his  calculation  of  the  distances  between  atoms,  91. 

Cell,  a,  the  primary  basis  of  organization,  208. 

Chemical  action  determined  by  the  molecular  velocity  and 
mass,  204. 

Chemical  action  is  due  to  a  change  in  the  molecular  atmos- 
pheres, 200. 

Chemical  affinity  not  an  inherent  principle,  157. 

Chemistry,  history  of,  202. 

Clairant,  his  problem  of  the  three  bodies,  179. 

Clapeyron,  his  thermo-dynamic  theory,  104. 

Clausius,  his  theory  of  gases,  115. 

Climate,  effect  of,  on  human  temperature,  214. 

Cohesion,  compared  with  gravity,  158. 

Cohesion  may  result  from  the  common  velocity  imparted  to  the 
molecules  of  a  body,  34. 

Cohesion  takes  place  <?nly  when  the  ethereal  atoms  touch  each 
other,  199. 

Comets,  do  they  prove  a  resisting  medium  ?  166. 

Copper,  sulphate  of,  its  action  on  the  transmission  of  light,  92. 

Cuvier  limits  the  relations  of  cause  and  effect  to  the  phenomena 
of  shock,  232. 

D. 

Democritus,  his  doctrine  regarding  atoms,  48. 
Descartes,  founder  of  analytical  geometry,  174. 
Descartes,  similarity  of  his  system  to  that  of  Epicurus,  49. 


246  INDEX. 

Difficulty  of  expressing  new  ideas  by  means  of  old  terms,  50. 
Du  Bois  Reymond,  his  theory  of  innervation,  226. 
Dulong  and  Petit,  law  of  gases,  nS. 

Dupre,  his  experiments  showing  the  force  of  cohesion,  158. 
Duration  of  waves  of  light  of  the  different  colors,  70. 
Dutrochet,  discoveries  of,  207. 


E. 

Eccentricity  of  the  earth's  orbit,  periodicity  of,  181. 

Egyptian  hieroglyphics,  key  to  discovered  by  Thomas  Young,  68. 

Electric  current,  136. 

Electric  fluid,  a  transport  of  ether,  141. 

Electric  motion  does  not  take  place  in  a  vacyum,  145. 

Electric  motion  similar  to  the  flowing  of  a  fluid,  139. 

Electric  spark  shows  that  the  fluid  passes  in  one  direction 
only,  142. 

Electric  unit,  determination  of,  148. 

Electricity,  a  duality  of  fluids  discussed,  126. 

Electricity,  its  mechanical  action,  150. 

Electricity,  its  relation  to  light,  150. 

Electricity,  not  an  entity,  but  a  motion,  127. 

Electricity,  velocity  of,  152. 

Electricity,  velocity  of,  through  nerves,  227. 

Elementary  bodies,  composed  of  ethereal  atoms,  195. 

Elementary  bodies,  variety  of,  due  to  motion,  195. 

Empedocles,  four  elements  of,  13. 

Energy,  active  and  potential,  242. 

Energy,  conservation  of,  242. 

Epicurus  constructs  an  atomic  theory,  48. 

Essences,  doctrine  of,  197. 

Ether  constitutes  the  atoms  of  bodies,  74. 

Ether  harmonizes  the  doctrines  of  Newton  and  Descartes,  185. 

Ether  is  imponderable,  75. 

Ether  is  the  cause  of  gravity,  96. 

Ether  the  sole  material  substance,  12,  38. 

Ether,  objections  to,  164. 

Ether,  objections  to,  answered,  168. 

Ethereal  atoms,  their  rotation  the  cause  of  their  transverse  vi- 
bration, 81. 

Euler.  his  arguments  against  the  emission  theory,  65. 


INDEX.  247 

F. 

Favre,  experiments,  149. 

Fermat,  founder  of  infinitesimal  calculus,  174. 

Fizeau,  M.,  his  explanation  of  light  fringes,  68. 

Force,  living,  determination  of,  in  mechanics,  108. 

Force,  that  which  causes  one  motion  to  give  place  to  another.  32. 

Force,  unity  of,  10. 

Foucault,  his  explanation  of  the  cause  of  light  fringes,  68. 

Fraunhofer,  lines  of,  94. 

Fresnel,  as  a  man  of  science,  88. 

Fresnel,  his  theory  of  the  vibration  of  the  ether,  80. 

G. 

Galileo  on  the  law  of  acceleration  of  falling  bodies,  174. 

Galvanometer,  the,  as  a  measure  of  electrical  phenomena,  133. 

Gases  all  contain  same  number  of  molecules  at  equal  pressure 
and  density,  116. 

Gases,  co-efficient,  of  the  expansion  of,  118. 

Gases,  molecular  arrangement  of,  when  they  pass  into  the  liquid 
and  solid  states,  112. 

Gases,  motion  of  their  molecules,  m. 

Gases,  why  attraction  does  not  exist  among  the  molecules  of,  HI. 

Gay-Lussac,  his  law  of  gaseous  mixtures,  117. 

Geisslers  tubes,  138. 

Germination,  mode  of,  209. 

Gravity  explained  by  the  doctrine  of  an  ether,  161. 

Gravity,  phenomena  of,  are  caused  by  the  pressure  of  the  ether 
upon  the  atoms  of  bodies,  37. 

Gravity,  unsoundness  of  the  usual  ideas  regarding  its  nature,  36. 

Grimaldi,  phenomena  of  interference,  his  experiment  to  pro- 
duce, 67. 

H. 

Hartmann,  his  theory  of  the  ether,  15. 

Heat  and  mechanical  force  mutually  equivalent,  23. 

Heat,  animal,  amount  evolved  in  birds,  220. 

Heat,  animal,  loss  of,  equal  to  that  produced  within  the  body,  214. 


248  INDEX. 

Heat,  animal,  mechanical  equivalent  of,  215. 

Heat,  animal,  the  result  of  the  oxidation  of  tissues,  213. 

Heat  is  a  motion,  106. 

Heat,  its  material  nature  discussed,  103. 

Heat,  latent,  of  dilatation,  53,  121. 

Heat,  mechanical  equivalent  of,  33. 

Heat,  point  of  maximum  intensity  beyond  the  visible  spec- 
trum, 61. 

Heat  units,  number,  produced  hourly  in  man,  213. 

Heat  units,  number  of,  produced  in  the  human  body  per  day,  217. 

Helmholtz,  his  experiments  on  muscular  contraction,  223. 

Heraclitus  regards  fire  as  the  sole  principle  of  the  universe,  47. 

Hirn,  M.,  his  notion  of  physical  forces  as  the  primordial  es- 
sences, 237. 

Hirn,  M.,  researches  upon  animal  heat,  215. 

Human  body,  composed  of  fourteen  elements,  210. 

Huyghens,  his  theory  of  central  forces,  174. 

Huyghens  proves  mathematically  the  undulatory  theory  of 
light,  65. 


I. 

Interferences,  luminous,  doctrine  of,  explained,  69. 
Interferences,  sonorous,  illustrated,  71. 


J. 

Jenkin,  Fleeming,  his  report  on  submarine  cables,  132. 

Joule,  M.,  his  determination  of  the  principle  of  the  convertibility 
of  heat  and  mechanical  force,  24. 

Joule,  M.,  his  discovery  of  the  mechanical  equivalent  of 
heat,  104. 

Joule,  M.,  his  experiment  showing  that  the  loss  of  heat  in  ex- 
pansion is  due  to  work,  122. 

Joule,  M.,  his  theory  of  gases,  115. 

Jupiter,  perturbations  of  his  orbit,  180. 


INDEX.  249 


K. 

Kepler,  discovery  of  his  first  law,  129. 

Kepler,  his  description  of  the  discovery  of  his  third  law,  172. 

Kepler,  his  mysticism,  173. 

Kepler,  his  theory  of  solar  attraction,  173. 


Laplace  considered  heat  material,  103. 
Laplace,  his  nebular  hypothesis,  186. 
Laplace  proves  the  stability  of  the  solar  system,  180. 
Lavoisier,  his  memoir  on  heat,  102. 
Leibnitz,  his  theory  of  the  ether,  15. 
Leucippus,  his  theory  of  the  universe,  48. 
Life  a  succession  of  motions.  210. 
Light,  duration  of  waves  of  the  different  colors,  70. 
Light,  its  resolution  by  means  of  a  prism  of  bi-sulphide  of  car- 
bon, 60. 

Light,  its  transmission  through  colored  media,  92. 
Light,  Newton's  theory  of,  64. 
Light,  undulation  of  waves  of,  transversal,  79. 
Light,  velocity  of,  70,  152.  . 


M. 

Malebranche,  one  of  the  first  to  regard  light  as  the  undulations  of 

an  ether,  65. 

Matter,  an  aggregate  of  ethereal  atoms,  39. 
Matter,  indestructibility  of,  31. 
Matter,  unity  of,  n. 

Matteucci,  his  calculation  of  the  work  done  by  muscles,  229. 
Marriotte's  law,  116. 
Mayer,  Dr.,    determines   the  mechanical  equivalent  of  heat,  9, 

24,  105. 

Mechanique  Celeste,  the,  188. 
Metals,  derived  from  a  single  base,  n. 

Metals,  conductibility  of,  149.  '     • 

Metals,  their  different  calorific  capacity,  132. 


25O  INDEX. 

Molecular  spaces,  their  relation  to  the  size  of  the  molecules,  90. 
Molecules,  effect  of  their  shape  on  the  passage  of  the  luminous 

rays,  92. 

Molecules,  structure  and  properties  of,  due  to  motion,  197. 
Motion,  never  created  or  destroyed,  32. 

Muscles  absorb  oxygen,  and  give  out  carbonic  acid  in  action,  223. 
Muscles,  effect  of  electricity  on,  223. 

Muscles,  Energy  of,  proportioned  to  activity  of  oxidation,  224. 
Muscles,  structure  and  contraction  of,  222. 


N. 

Nature,  activity  of,  consists  in  turning  vis  viva  into  work,  109. 

Nebular  hypothesis,  186. 

Nerves  excite,  but  are  not  the  cause  of  muscular  energy,  228. 

Nerves,  structure  and  function  of,  225. 

Nerves,  their  mode  of  action,  226. 

Nerves,  their  work  compared  with  that  of  muscles,  229. 

Nervous  currents  compared  with  electric  currents,  227. 

Newton,  his  belief  in  the  existence  of  an  ether,  13. 

Newton,  his  emission  theory  of  light,  64. 

Newton,  his*  quarrel  with  Leibnitz,  179. 

Newton,  his  views  on  the  nature  of  gravity,  155. 

Newton,  manner  in  which  he  discovered  law  of  gravity,  175. 


o. 

Orpheus,  his  reference  to  the  ether,  13. 

P. 

Philosopher,  the  physical,  has  to  do  with  apparent,  not  absolute 
relations,  240. 

Plateau,  his  experiment  to  prove  the  nebular  hypothesis,  188. 

Pltlcher's  tubes,  145. 

Poinsot  shows  how  the  ethereal  atoms  may  rebound  without  be- 
ing elastic,  77. 

Polarization,  mode  of,  described,  86. 


INDEX.  25 1 

Polarization,  its  phenomena  explained  by  the  theory  of  transverse 

vibrations,  87. 

Popular  Science  Monthly,  reference  to,  12. 

Potash,  permanganate  of,  extinguishes  the  red  and  blue  rays,  92. 
Pressure,  constant,  its  relation  to  heat  capacity,  121. 
Prism,    how  its    nature   affects  to   location    of  the    maximum    of 

heat,  63. 

Protoplasm,  208. 
Prout,  his  law,  194. 

Q- 

Quinine,  sulphate  of,  its  action  upon  the  spectrum,  62. 

R. 

Red,  the'color,  number  of  light  vibrations  necessary  to,  70. 
Regnault,  his  contribution  to  thermo-dynamics,  119.' 
Resistance  to  submarine  cables,  119. 

Rock  salt,  prism  composed  of,  its  effect  upon  the  solar  beam,  63. 
Rumford,  Count,  his  experiment  to  show  that  heat  is  not  mate- 
rial, 103. 

s. 

Saigey,  Emile,  his  idea  of  the  ether  as  the  constitutive  element  of 
matter,  17. 

Saigey,  Emile,  phenomena  of  organic  life  obedient  to  the  laws  of 
mechanics,  18. 

Saturn,  perturbations  of  his  orbit, "181. 

Secchi,  Father,  concerning  transverse  motion  of  light,  81. 

Secchi,  Father,  his  treatise  upon  the  unity  of  the  physical 
forces,  26. 

Secular  inequalities,   178. 

Seguin,  essay  on  railroads,  104. 

Senarmont,  M.  De,  regards  physical  phenomena  as  the  manifesta- 
tions of  a  single  agent,  234. 

Similarity  of  animal  and  vegetable  structure,  206. 

Soul,  problems  of  the,  independent  of  the  laws  of  physics,  239. 

Sound,  analogies  between  it  and  light,  56. 

Sound,^  mechanical  equivalent  of,  difficult  to  determine,  58.       • 

Sound,*  the  effect  of  vibrations,  55. 


252  INDEX. 

Sound,  undulation  of  waves  of  longitudinal,  79. 

Spark,  electric,  stratification  of,  193. 

Spectrum,  analogy  between  its  colors  and  harmonious  sounds,  94. 

Spectrum,  continuous,  how  produced,  93. 

Spectrum,  its  invisible  calorific  and  chemical  portions,  62. 

Spectrum,  reversement  of,  95. 

Spiller,  Philip,  his  theory  of  the  ether,  15. 

Substitution,  law  of,  203. 

Swedenborg  on  the  ether,  14. 

Swedenborg  on  the  luminiferous  ether,  164. 


T. 

Temperature,  absolute  zero  of,  120. 

Temperature  produces  changes  in  the  form  of  bodies,  no. 

Thales  made  water  the  principle  of  all  things,  46. 

Theories,  their  use  in  scientific  investigations,  44. 

Thermo-electric  pile,  145. 

Top,  experiment  with,  illustrating  lateral  displacement,  80. 

Translation  of  atoms,  motion  of,  78. 

Transversal  vibrations  extinguished  in  conducting  bodies,  153. 

Tyndall,  concerning  vibration  of  atoms,  77. 

Tyndall,  estimate  of  his  work,  "Heat  as  a  Mode  of  Motion,"  99. 

Tyndall,  his  experiment  with  compressed  air,  123. 

Tyndall,  on  the  luminiferous  ether,  15. 


u. 

Units,  electric,  necessity  of  determining,  130. 
Units,  their  importance  in  physics,  128. 
Unity  of  physical  forces,  an  ancient  doctrine,  46. 
Universe,  author's  theory  of,  189. 


V. 

Verdet,  treatise  on  the  mechanical  theory  of  heat,  26. 
Vis  viva,  definition  of,  in  mechanics,  107. 

Vis  viva  of  the  heavenly  bodies  compared  with  that  of  mole- 
cules, 193. 


INDEX.  253 

Violet  color,  number  of  vibrations  necessary  to  cause,  7°« 
Vitality  considered  as  a  material  motion,  211. 
Voltameter,  the,  147. 
Volume,  constant,  its  relation  to  heat  capacity,  121. 


w. 

Water,  effect  of  passing  a  solar  beam  through  a  prism  of,  63. 
Whewell,  History  of  the  Inductive  Sciences,  13. 
Will,  the,  its  relation  to  mechanical  work,  230. 


x. 

Xenophanes,  his  doctrine  regarding  matter,  47. 

Y. 

Yellow,  the  color,  number  of  vibrations  necessary  to'produce,  70. 
Young,  Dr.  T.,  confirms  undulatory  theory  of  light,  "14. 


ERRATA. 


Page  18,  line  i$,for  organic  read  inorganic. 

"  41,  last  line,  supply  the  word  our  before  thought. 

"  47,  line  2,  for  Anaximine  read  Anaximines. 

"  48,  line  i8,/or  advantages  read  advantage. 

"  80,  line  18,  after  word  component  insert  of. 

"  81,  line  21,  for  good  read  goal. 

"  195,  line  19,  for  agreement  read  argument. 

The  notes  at  the  bottom  of  pages  78,  80,  86,  118,  120,  164,  are  by 

the  translator. 
The  note  at  the  bottom  of  page  188  is  by  the  author,  as  far  as 

"  The  reader  will  observe,"  etc. 


LITERARY  ITEMS 

AND 

SPUING  ANNOUNCEMENTS 

OF 

ESTES  &  LAURIAT. 

We  earnestly  request  ISooTtscllers  to  examine 
this  list,  and  send  iis  advance  orders,  that 
they  may  receive  the  new  books  promptly. 

We  shall  publish  at  an  early  day 

GUiZOT'S  POPULAR 

HISTORY  OF  FRANCE, 

FROM  THE  EARLIEST  TIMES  TO  THE  PRESENT, 

This  work  is  the  result  of  the  labor  of  years,  and 
the  research  of  a  long  life  of  one  of  the  greatest 
statesmen  and  historians  of  France. 

The  London  Times  says :  "  There  are  few  guides  so 
trustworthy,  and  none  who  interpret  history  more 
faithfully,  than  the  illustrious  author  of  The  History 
of  Civilization.  The  work  will  supply  a  long-felt 
want,  and  ought  to  be  in  the  hands  of  all  students 
of  history." 

We  shall  publish  this  work  in  six  handsome  oc- 
tavo  volumes,  with 

Two  Hundred  Illustration*. 

We  believe  this  will  be  the  handsomest  history 
erer  published  in  this  country. 

Price  per  vol.,  $3.50. 


IMPOBTANT  ATOOOTOEMEffTS, 

By  arrangement  with  the  author,  a  volume  of 

LECTURES  AND  SERMONS 

BY  THE 

REV.  W.  MOELEY'PUNSHON,  LL.D. 

This  volume  will  conlain  his  most  celebrated  lec- 
tures, "  The  Huguenots,"  "  Macaulay,"  "  Wes- 
ley  and  his  Times,"  "Florence  and  Flor- 
entines," "  Daniel  in  Babylon,"  &c.,  and  will 
he  printed  on  fine  tinted  paper,  and  bound  with  hand- 
some gilt  side,  back,  and  top.  It  will  also  contain  a 
tine  steel  portrait. 

Price  $2.50. 

Over  4000  of  this  volume  have  already  been  ordered 
in  advance  of  publication. 

NOW    RJEADY, 

Shaw's  Tourist's  Picturesque  Guide 

TO 

GREAT  BRITAIN  AND  IRELAND. 

Prepared  expressly  for  the  use  of  American  Trav- 
ellers.   It  contains  96  Colored  Plates,  and  a  large 
uumber  of  Engravings,  New  Maps,  &c. 
IGmo,  cloth  gilt.    $4.00. 


NOW  READY, 

An  Entirely  New  and  Important  Work. 
A  HAND-BOOK 

OF 

Hardy  Trees,  fe$ln*ubs, 

AND 

HERBACEOUS    PLANTS. 

Containing  Descriptions,  Native  Countries,  &e.,  of 

the  best  species  in  cultivation;  together  with 

cultural  details,  comparative  hardiness, 

suitability  for  particular  positions, 

&e.,  based  on  the  French  work  of 


OF  THE  INSTITUTE  OF   FEANOE. 

BY    W.    B.    HELMSLEY, 

Assistant  at  the  Royal  Gardens,  Kew. 
WITH 

-A.3ST   ITsTT^J-OIDTJCTIOlSr 

BY  EDWARD  S.  RAND,  JR., 

Author  q/""  Flowers  for  Parlor  and  Garden,"  fyc. 
AND 

Three  Hundred  Fine  Illustrations. 

I  vol.,  8vo,  700  pages.    $7.50. 


4 


PKOF.  A.  S.  PACKARD'S 
BOOKS    ON  ENTOMOLOGY. 


HALF  HOURS  WITH  INSECTS. 

A  popular  introduction  to  the  study  of  this  inter- 
esting science.  Will  be  published  iu  12  parts,  25  cts. 
per  part,  or  $  >.50,  in  advance,  for  the  twelve.  It  will 
contain  one  Colored  Plate,  and  a  large  number  of 
Illustrations.  This  will  be  Vol.  I.  of  a  series, to  be 
entitled 

Half-Hour  Recreations  ia  Natural  History, 

and  will  soon  be  followed  by  others. 
ALSO  IN   PII  ESS, 

OUR    COMMON    INSECTS. 

A  popular  account  of  the  more  common  insects  of 
our  country,  embracing  chapters  on 

Uees  and  their  1'urasitcs,  Moths,  Flies, 
Mosquitoes,  beetles,  &c., 

while  a  Calendar  will  give  a  general  account  of  the 
more  common  injurious  and  beneficial  insects,  and 
their  time  of  appearance,  habits,  etc.  200  pages,  pro- 
fusely illustrated.  Price  $2.50. 

Just  Published,  a  New  and  Improved  Edition  of 

PACKARD'S 
GUIDE  TO  THE  STUDY  OF  INSECTS. 

700  Illustrations,  8vo.    Price  reduced  to  $5.00. 
This  book  is  now  acknowledged  to  be  the  standard, 
and  is  used  in  the  leading  universities  and  institutions 
ef  Europe  and  America. 


Important  Ornithological  Publications, 

KEY  TO  NORTH  AMERICAN  BIRDS. 

By  Elliott  Coues,  M.  D.  369  imperial  octavo  pages. 
Illustrated  by  6  Steel  Plates  and  238  Wood  Cuts.  A 
manual  or  text-book  of  the  Birds  of  North  America, 
containing  a  Synopsis  of  Living  and  Fossil  Birds,  and 
descriptions  of  every  North  American  species  known 
to  this  time.  Price  $7.00. 


BAIRD    AND    CASSINS' 
IVORTH  AJMIE11IOAJ 

With  1OO  Colored  Plates. 

This  work  contains  descriptions  of  100  Species  of 
Birds  not  figured  by  Audubon.  It  is  now  nearly  out 
of  print,  but  few  copies  of  the  edition  remaining  un- 
sold. 2  vols.,  quarto.  $20.00. 

THE   BIRDS  OF   FLORIDA. 

By  C.  J.  Maynard.  This  work  will  be  issued  to 
subscribers  in  parts.  Price  $1.00  for  each  Part,  pay- 
able on  delivery,  or  $10.00  in  advance  for  the  com- 
plete work.  The  work  will  consist  of  at  least  twelve 
parts,  and  will  make  a  volume  of  about  Three  Hun- 
dred Large  Quarto  Pages,  containing  Five  Colored 
Plates  of  new  or  little  known  species  of  Birds  and 
Eggs.  Upwards  of  250  species  of  Birds  found  in 
Florida  by  the  author,  will  be  described. 

THE  AMERICAN  NATURALIST. 

An   Illustrated    Repertory   of    Natural   History. 
Making  a  compact    library  of  popular   papers  on 
nearly  every  branch  of  this  interesting  science. 
6  vols.,  8vo,  cloth.    $5.00  per  vol. 


4 


•i  H 


SCIENTIFIC  BOOKS  IN  PRESS. 

We  shall  also  publish  at  an  early  day,  by  arrange 
ment, 

THE  EARLY  HISTORY  OF  MANKIND 

And  Development  of  Civilization,  1  vol.  8vo.,  $2.50; 

AND 

PRIMITIVE  CULTURE, 

Researches  into   the   Development   of  Mythology, 
Philosophy,  Religion,  Art,  said  Custom. 

By    EDWARD    IB.   TYLOR, 

Author  of  "Mexico  and  the  Mexicans." 
2  volumes,  8vo.    $5.00. 


NOW    READY, 

SPECTRUM   ANALYSIS 
EXPLAINED. 

An  explanation  of  this  wonderful  discovery,  and 
Its  uses  to  science,  including  the  received  Theory  of 
Sound,  Heat,  Light,  and  Color:  with  chapters  on 
the  Sun,  Stars.  Nebulae,  Comets,  and  Meteoric  Show- 
ers. Abridged  from  the  works  of  Schclien,  lloecoe, 
Huggms,  Lockyer,  Young,  and  others,  by  the  editor 
of  "Half  Hour  Recreations  in  Popular  Science." 

12mo,  cloth,  with  two  colored  plates  »nd  twentr 
illustrations.  $1.50. 


Books  Recently   Issued. 
]M  TJ  R  I*  H  Y»8 

Critical  Commentary  on  Genesis. 

With  an  INTRODUCTION  by  Prof.  Alvah  Hovey,  D.D., 

of  Newton  Theological  Seminary,  and  a  PREFACE 

by  Rev.  J.   P.  Thompson,  D.  D.,  of  Tabernacle 

Church,  New  York.  One  vol.,  crown  8vo.    $2.50. 

The  most  valuable  contribution  that  has  for  a  long 

time  been  made  to  the  many  aids  for  the  study  of  the 

Old  Testament,  is    Dr.  Murphy's    Commentary    on 

Genesis.    This  volume  is  racy  and  readable,  as  well 

as  reliable.  It  is  a  good  deal  to  say  of  a  commentary, 

but  we  say  it  in  all  sincerity,  that  it  furnishes  about 

as  fascinating  work  for  one's  hours  of  reading  as  any 

volume  of  the  day,  in  any  department  of  literature. 

—  Congregationalist. 

JERUSALEM  rAncient  &  Modern. 

By  Rev.  I.  P.  WARREN,  D.  D. 

Being  a  complete  and  compact  history,  description, 
and  illustration  of  the  Holy  City,  including  the  Top- 
ography, present  condition  of  the  city  and  surround- 
ings; the  principal  points  of  interest  of  both  the 
ancient  and  modern  city;  the  recent  explorations 
and  excavations,  and  a  full  description  of  the  Tem- 
ple. It  is,  in  fact,  an  epitome  of  reliable  information 
on  the  subject  gathered  from  majiy  valuable  books, 
not  accessible  to  general  readers. 

1  vol.,  8vo,  tinted  paper,  bevelled  boards,  with  two 
Key  Plates,  and  several  Illustrations.  $1.25. 


A  New  American  Novel.    By  Miss  E.  B.  Emery. 

12mo,  cloth.    $1.50. 

This  book  is  pronounced  by  good  literary  judgee  to 
be  a  remarkably  interesting  one. 


RECREATIONS  IN  POPULAR  SCIENCE. 

Edited   by   DANA    ESTES. 

The  growing  demand  in,  this  country  for  books  on 
popular  science,  encourages  the  editor  and  publish- 
ers to  issue  this  series  of  papers,  compiled  from  the 
works  of  the  most  popular  scientific  writers. 

25  cts.  per  Part;  $2.50  for  12  consecutive  Parts. 

No.  1.  Strange  Discoveries  respecting  the 
Aurora  and  recent  Solar  Researches.  By 
Richard  A.  Proctor,  F.  R.  A.  S. 

No.  2.  The  Cranial  Affinities  of  Man  and 
the  Ape.  By  Prof.  Rudolph  Virchow,  of  Berlin, 
author  of  "  Cellular  Pathology."  Fully  Illustrated. 

No.  3.  Spectrum  Analysis  Explained,  and 
its  Uses  to  Science  Illustrated.  With  a  Colored 
Plate  and  several  Wood  Cuts. 

No.  4.  Spectrum  Analysis  Discoveries, 
showing  its  Application  in  Microscopical  Research, 
and  to  Discoveries  of  the  Physical  Constitution  and 
Movements  of  the  Heavenly  Bodies.  From  the 
works  of  Schellen,  Young,  Roscoe,  Lockyer,  Hug- 
gins,  and  others. 

No.  5.  Nebulae,  Meteoric  Showers,  and 
Comets. 

No.  fl.  Unconscious  Action  of  the  Brain, 
and  Epidemic  Delusions.  By  Dr.  Carpenter, 
author  of  "  The  Microscope  and  its  Revelations," 
"  Human  Physiology,"  &c. 

No.  7.  The  Geology  of  the  Stars.  By  Prof. 
A.  Winohell,  of  the  University  of  Michigan,  author 
of"  Sketches  of  Creation." 

No.  8.   On  Yeast.    By  Prof.  Huxley,  F.  R.  S. 

No.  9.  The  Circulation  of  the  Waters  on 
the  Face  of  the  Earth.  By  Prof.  H.  W.  Dove. 

No.  10.  The  Stone  Age,  Past  and  Present. 
By  Edward  B.  Tylor,  author  of  "Primitive  Culture." 

No.  11.  The  Relation  between  Matter  and 
Force.  By  Prof.  John  H.  Tice,  of  St.  Louis. 


•©• 


ESTES  &  LAURIAT'S 
RECENT     IMPORTATIONS 

OF 

STANDARD    BOOKS. 


HOGARTH'S  WOEKS.  Quarto,  cloth.  With 
62  full-page  Plates,  and  descriptive  letter- 
press. "  A  marvel  of  cheapness."  .....  $3.50 

EASTLAKE'S  HINTS  on  Household  Taste 
in  Furniture,  &,c.  Third  London  Edirion. 
Revised.  Crown  8vo,  cloth,  red  edges,  .  .  .  6.00 

GWILT'S   ENCYCLOPEDIA    OF    ARCHI- 
TECTURE.   With  above  1600  Wood  Cuts. 
Fifth  edition,  with  Alterations  and  consider- 
able Additions,  by  Wyatt  Papworth.    Svo. 

Cloth,     .................    20.00 

Half  Russia,    ..............    26.00 

FROUDE'S  HISTORY  OF  ENGLAND,  from 
the  Fall  of  Wolsey  to  the  Defeat  of  the  Span- 
ish Armada.     By  James  Anthony  Froude, 
M.  A.    Cabinet  edition.   12  vols.  Crown  Svo. 

Cloth,  ..................  27.00 

Half  calf,  extra,  .............  4s.oo 

Full  tree  calf,  ..............   03.00 

TALES   FROM  BLACKWOOD.    A  selection 
of  the    choicest    stories  from  this  best  of 
magazines. 

6  vols.,  cloth,   ..............     <».oo 

ft    '       half  Roxburgh,  .........   1^.00 

6    "          '•     calf,     ............    16.00 


IMPORTED   BOOKS. 


CHAMBERS'  E1V CYCLOP JEI»I A.  A  Dic- 
tionary of  Universal  Knowledge,  in  which  the  facts 
of  Science,  Philosophy,  History,  and  even  mat- 
ters of  Familiar  Conversation,  are  given  in  a  man- 
ner adapted  for  easy  consultation.  Profusely  Il- 
lustrated by  Wood  Engravings  and  Maps.  This 
comprehensive  and  elaborate  work  is  now  complete 
in  10  volumes,  8vo. 

Cloth,  including  Maps, $45.00 

Half  call',  marble  edges,  including  Maps,    65.00 
"    Morocco,  extra, 70.00 

3IOUAL    EMBLEMS.    With   Aphorisms,  Ad- 
ao-es  and  Proverbs,  of  all  Ages  and  Nations.   From 
J.  Cats  and  Robert  Fairlie.    With  Illustrations  by 
John  Leighton,  F.  S.  A.    Quarto. 
Full  gilt,  cloth,  extra, $12.00 

MRS.  AJSXA.  JAMESON'S  WORKS  O1V 
SACREO  ART,  as  follows:  — 

Sacred  and  Legendary  Art.  Illustrated 
with  19  Etchings  and  187  Wood  Engravings.  2vols. 

Legends  of  the  Monastic  Orders.  Illus- 
trated with  1 1  Etchings  and  88  Wood  Engravings. 

Legends  of  the  Madonna.  Illustrated  with 
27  Etchings  and  165  Wood  Engravings. 

The  History  of  Our  Lord,  as  exemplified 
in  Works  of  Art.    Illustrated  with  31  Etchings 
and  281  Wood  Engravings.    2  vols. 
In  all  0  vols.,  demy  4to.  "* 

Cloth, $40.00 

Half  calf,  gilt  tops, 65.00 

"     Morocco, 67.50 

Tree  calf, 75.00 

Morocco,  extra,  gilt  edges 100.0» 


IMPORTED  BOOKS. 


STRICKLAND'S  QUEENS  OF  ENGLAND. 

A  new  edition,  the  best  in  the  market.  Revised 
and  greatly  augmented;  with  a  Portrait  of  every 
Queen.  8  vols.,  8vo. 

Cloth,  uncut, $25.00 

Half  calf, 40.00 

Tree  calf  (by  Reviere),   50.00 

URE'S    DICTIONARY 

Of  Arts,  Manufactures,  and  Mines.  Sixth 
edition.  Re-written  and  greatly  enlarged  by  Robert 
Hunt  F.  R.  S.,  assisted  by  numerous  contributors. 
With  2000  Wood  Cuts.  3  vols.,  8vo.  Cloth,  $25.00; 
half  Russia,  extra,  $37.00. 

NASH'S  MANSIONS  OF  ENGLAND, 

In  the  Olden  Time.  Re-edited  by  J.  Corbet 
Anderson.  With  101  elegant  Illustrations.  4  vols. 
bound  in  2.  Half  Mor.,  gilt  edges  and  sides,  $75.00; 
full  Levant  Mor.,  extra,  $90.00. 


LIFE  OF  MAN, 

Symbolized  by  the  Months  of  the  Year,  in  their  Sea- 
sons and  Phases,  with  Passages  selected  from  the 
Ancient  and  Modern  Authors.  By  Richard  Pigott. 
Accompanied  by  a  series  of  25  full-page  Illustrations, 
and  many  hundred  Marginal  Devices,  decorated  Ini- 
tial Letters  and  Tail-Pieces,  engraved  on  wood  from 
original  designs  by  John  Leighton.  1  vol.,  quarto. 
Cloth,  full  gilt,  extra,  $12.00. 


IMPORTED    BOOKS. 

-OOXKOO 

Choice   Editions 

OF 

WAVERLEY  NOVELS, 

Published  by  the  Proprietors  of  the  Copyright, 
Messrs.  BLACK  &  Co.,  of  Edinburgh. 


Cheap  Edition,  4  vols.,  complete,  half  calf,  sprin- 
kled edges, $15.00 

The  same,  half  calf,  gilt,  extra, 18.00 

Handy  Edition,  12  vols.,  half  calf,  cloth  sides,    25.00 
"  "         12    "         "       "  marbl'd  edges,  25.00 

Centenary  Edition,  25  vols.,  cloth, 31.25 

"  "         25     "       half  Roxburgh,       50.00 

"  «        25     «        "    calf,  extra,        75.00 

"  "         25     "        «    Morocco,  gilt 

tops, 85.00 

Library  Edition,  25   vols.,  8vo.,  beautifully 
Illustrated  with  204  Steel  Plates,  half  calf,  100.00 

The  same,  half  Morocco, 120.00 

"         "     tree  calf,  extra 160.00 

"     full  Morocco,  extra, 175.00 


14  DAY  USE 

RETURN  TO  DESK  FROM  WHICH  BORROWED 

LOAN  DEPT. 

This  book  is  due  on  the  last  date  stamped  below,  or 

on  the  date  to  which  renewed. 
Renewed  books  are  subject  to  immediate  recall. 


OHM  IF #3877. 


IAY  2  8  1977 


•'-     '.* 


LD  21A-50m-8,'61 
(Cl795slO)476B 


General  Library 
University  of  California 
Berkel 


C.BERKELEY  LIBRARIES 


861372 


THE  UNIVERSITY  OF  CALIFORNIA  LIBRARY 


